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\chapter{Proxies}
Proxy configuration can be located in a set of sections:
\begin{itemize}
\item[-] defaults <name>
\item[-] frontend <name>
\item[-] backend <name>
\item[-] listen <name>
\end{itemize}
\begin{description}
\item[A "defaults" section] sets default parameters for all other sections following
its declaration. Those default parameters are reset by the next "defaults"
section. See below for the list of parameters which can be set in a "defaults"
section. The name is optional but its use is encouraged for better readability.
\item[A "frontend" section] describes a set of listening sockets accepting client
connections.
\item[A "backend" section] describes a set of servers to which the proxy will connect
to forward incoming connections.
\item[A "listen" section] defines a complete proxy with its frontend and backend
parts combined in one section. It is generally useful for TCP-only traffic.
\end{description}
\index{proxy}
All proxy names must be formed from upper and lower case letters, digits,
'/verb|-|' (dash), '\verb|_|' (underscore) , '\verb|.|' (dot) and '\verb|:|' (colon). ACL names are
case-sensitive, which means that "www" and "WWW" are two different proxies.
Historically, all proxy names could overlap, it just caused troubles in the
logs. Since the introduction of content switching, it is mandatory that two
proxies with overlapping capabilities (frontend/backend) have different names.
However, it is still permitted that a frontend and a backend share the same
name, as this configuration seems to be commonly encountered.
Right now, two major proxy modes are supported: "tcp", also known as layer 4,
and "http", also known as layer 7. In layer 4 mode, HAProxy simply forwards
bidirectional traffic between two sides. In layer 7 mode, HAProxy analyzes the
protocol, and can interact with it by allowing, blocking, switching, adding,
modifying, or removing arbitrary contents in requests or responses, based on
arbitrary criteria.
\section{Proxy keywords matrix}
The following list of keywords is supported. Most of them may only be used in a
limited set of section types. Some of them are marked as "deprecated" because
they are inherited from an old syntax which may be confusing or functionally
limited, and there are new recommended keywords to replace them. Keywords
marked with "(*)" can be optionally inverted using the "no" prefix, eg. "no
option contstats". This makes sense when the option has been enabled by default
and must be disabled for a specific instance. Such options may also be prefixed
with "default" in order to restore default settings regardless of what has been
specified in a previous "defaults" section.
\begin{longtable}{|lr|c|c|c|c|}
\hline
\head{Keyword}&\head{Mark}&\head{Defaults}&\head{Frontend}&\head{Listen}&\head{Backend}\\
\hline
\input{keyword_matrix}
\end{longtable}
\section{Alphabetically sorted keywords reference}
This section provides a description of each keyword and its usage.
\subsubsection[acl]{acl <aclname> <criterion> [flags] [operator] <value> ...}
\index{acl}
Declare or complete an access list.
\dflb{no}{yes}{yes}{yes}
Example:
\begin{verbatim}
acl invalid_src src 0.0.0.0/7 224.0.0.0/3
acl invalid_src src_port 0:1023
acl local_dst hdr(host) -i localhost
\end{verbatim}
See section 7 about ACL usage.
\subsubsection[appsession]{appsession <cookie> len <length> timeout <holdtime> [request-learn] [prefix] [mode <path-parameters|query-string>]}
\index{appsession}
Define session stickiness on an existing application cookie.
\dflb{no}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<cookie>] this is the name of the cookie used by the application and which
HAProxy will have to learn for each new session.
\item[<length>] this is the max number of characters that will be memorized and
checked in each cookie value.
\item[<holdtime>] this is the time after which the cookie will be removed from
memory if unused. If no unit is specified, this time is in
milliseconds.
\item[request-learn]
If this option is specified, then haproxy will be able to learn
the cookie found in the request in case the server does not
specify any in response. This is typically what happens with
PHPSESSID cookies, or when haproxy's session expires before
the application's session and the correct server is selected.
It is recommended to specify this option to improve reliability.
\item[prefix] When this option is specified, haproxy will match on the cookie
prefix (or URL parameter prefix). The appsession value is the
data following this prefix.
Example:
\verb|appsession ASPSESSIONID len 64 timeout 3h prefix|
This will match the cookie ASPSESSIONIDXXXX=XXXXX,
the appsession value will be XXXX=XXXXX.
\item[mode] This option allows to change the URL parser mode.
2 modes are currently supported:
\begin{itemize}
\item[-] path-parameters:
The parser looks for the appsession in the path parameters
part (each parameter is separated by a semi-colon), which is
convenient for JSESSIONID for example.
This is the default mode if the option is not set.
\item[-] query-string:
In this mode, the parser will look for the appsession in the
query string.
\end{itemize}
\end{description}
When an application cookie is defined in a backend, HAProxy will check when
the server sets such a cookie, and will store its value in a table, and
associate it with the server's identifier. Up to <length> characters from
the value will be retained. On each connection, haproxy will look for this
cookie both in the "Cookie:" headers, and as a URL parameter (depending on
the mode used). If a known value is found, the client will be directed to the
server associated with this value. Otherwise, the load balancing algorithm is
applied. Cookies are automatically removed from memory when they have been
unused for a duration longer than <holdtime>.
The definition of an application cookie is limited to one per backend.
\emph{Note:}
Consider not using this feature in multi-process mode (nbproc > 1)
unless you know what you do: memory is not shared between the
processes, which can result in random behaviours.
\verb|appsession JSESSIONID len 52 timeout 3h|
See also : "cookie", "capture cookie", "balance", "stick", "stick-table",
"ignore-persist", "nbproc" and "bind-process".
\subsubsection[backlog]{backlog <conns>}
\index{backlog}
Give hints to the system about the approximate listen backlog desired size
\dflb{yes}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<conns>]
is the number of pending connections. Depending on the operating
system, it may represent the number of already acknowledged
connections, of non-acknowledged ones, or both.
\end{description}
In order to protect against SYN flood attacks, one solution is to increase
the system's SYN backlog size. Depending on the system, sometimes it is just
tunable via a system parameter, sometimes it is not adjustable at all, and
sometimes the system relies on hints given by the application at the time of
the listen() syscall. By default, HAProxy passes the frontend's maxconn value
to the listen() syscall. On systems which can make use of this value, it can
sometimes be useful to be able to specify a different value, hence this
backlog parameter.
On Linux 2.4, the parameter is ignored by the system. On Linux 2.6, it is
used as a hint and the system accepts up to the smallest greater power of
two, and never more than some limits (usually 32768).
See also : "maxconn" and the target operating system's tuning guide.
\subsubsection[balance] {balance <algorithm> [ <arguments> ]}
\subsubsection*{balance url\_param <param> [check\_post [<max\_wait>]]}
\index{balance}
Define the load balancing algorithm to be used in a backend.
\dflb{yes}{no}{yes}{yes}
Arguments:
\paragraph*{<algorithm>}
is the algorithm used to select a server when doing load
balancing. This only applies when no persistence information
is available, or when a connection is redispatched to another
server. <algorithm> may be one of the following:
\begin{description}
\item[roundrobin] Each server is used in turns, according to their weights.
This is the smoothest and fairest algorithm when the server's
processing time remains equally distributed. This algorithm
is dynamic, which means that server weights may be adjusted
on the fly for slow starts for instance. It is limited by
design to 4128 active servers per backend. Note that in some
large farms, when a server becomes up after having been down
for a very short time, it may sometimes take a few hundreds
requests for it to be re-integrated into the farm and start
receiving traffic. This is normal, though very rare. It is
indicated here in case you would have the chance to observe
it, so that you don't worry.
\item[static-rr] Each server is used in turns, according to their weights.
This algorithm is as similar to roundrobin except that it is
static, which means that changing a server's weight on the
fly will have no effect. On the other hand, it has no design
limitation on the number of servers, and when a server goes
up, it is always immediately reintroduced into the farm, once
the full map is recomputed. It also uses slightly less CPU to
run (around -1\%).
\item[leastconn] The server with the lowest number of connections receives the
connection. Round-robin is performed within groups of servers
of the same load to ensure that all servers will be used. Use
of this algorithm is recommended where very long sessions are
expected, such as LDAP, SQL, TSE, etc... but is not very well
suited for protocols using short sessions such as HTTP. This
algorithm is dynamic, which means that server weights may be
adjusted on the fly for slow starts for instance.
\item[first] The first server with available connection slots receives the
connection. The servers are choosen from the lowest numeric
identifier to the highest (see server parameter "id"), which
defaults to the server's position in the farm. Once a server
reaches its maxconn value, the next server is used. It does
not make sense to use this algorithm without setting maxconn.
The purpose of this algorithm is to always use the smallest
number of servers so that extra servers can be powered off
during non-intensive hours. This algorithm ignores the server
weight, and brings more benefit to long session such as RDP
or IMAP than HTTP, though it can be useful there too. In
order to use this algorithm efficiently, it is recommended
that a cloud controller regularly checks server usage to turn
them off when unused, and regularly checks backend queue to
turn new servers on when the queue inflates. Alternatively,
using "http-check send-state" may inform servers on the load.
\item[source] The source IP address is hashed and divided by the total
weight of the running servers to designate which server will
receive the request. This ensures that the same client IP
address will always reach the same server as long as no
server goes down or up. If the hash result changes due to the
number of running servers changing, many clients will be
directed to a different server. This algorithm is generally
used in TCP mode where no cookie may be inserted. It may also
be used on the Internet to provide a best-effort stickiness
to clients which refuse session cookies. This algorithm is
static by default, which means that changing a server's
weight on the fly will have no effect, but this can be
changed using "hash-type".
\item[uri] This algorithm hashes either the left part of the URI (before
the question mark) or the whole URI (if the "whole" parameter
is present) and divides the hash value by the total weight of
the running servers. The result designates which server will
receive the request. This ensures that the same URI will
always be directed to the same server as long as no server
goes up or down. This is used with proxy caches and
anti-virus proxies in order to maximize the cache hit rate.
Note that this algorithm may only be used in an HTTP backend.
This algorithm is static by default, which means that
changing a server's weight on the fly will have no effect,
but this can be changed using "hash-type".
This algorithm supports two optional parameters "len" and
"depth", both followed by a positive integer number. These
options may be helpful when it is needed to balance servers
based on the beginning of the URI only. The "len" parameter
indicates that the algorithm should only consider that many
characters at the beginning of the URI to compute the hash.
Note that having "len" set to 1 rarely makes sense since most
URIs start with a leading "\verb|/|".
The "depth" parameter indicates the maximum directory depth
to be used to compute the hash. One level is counted for each
slash in the request. If both parameters are specified, the
evaluation stops when either is reached.
\item[url\_param] The URL parameter specified in argument will be looked up in
the query string of each HTTP GET request.
If the modifier "check\_post" is used, then an HTTP POST
request entity will be searched for the parameter argument,
when it is not found in a query string after a question mark
('?') in the URL. Optionally, specify a number of octets to
wait for before attempting to search the message body. If the
entity can not be searched, then round robin is used for each
request. For instance, if your clients always send the LB
parameter in the first 128 bytes, then specify that. The
default is 48. The entity data will not be scanned until the
required number of octets have arrived at the gateway, this
is the minimum of: (default/max\_wait, Content-Length or first
chunk length). If Content-Length is missing or zero, it does
not need to wait for more data than the client promised to
send. When Content-Length is present and larger than
<max\_wait>, then waiting is limited to <max\_wait> and it is
assumed that this will be enough data to search for the
presence of the parameter. In the unlikely event that
Transfer-Encoding: chunked is used, only the first chunk is
scanned. Parameter values separated by a chunk boundary, may
be randomly balanced if at all.
If the parameter is found followed by an equal sign ('\verb|=|') and
a value, then the value is hashed and divided by the total
weight of the running servers. The result designates which
server will receive the request.
This is used to track user identifiers in requests and ensure
that a same user ID will always be sent to the same server as
long as no server goes up or down. If no value is found or if
the parameter is not found, then a round robin algorithm is
applied. Note that this algorithm may only be used in an HTTP
backend. This algorithm is static by default, which means
that changing a server's weight on the fly will have no
effect, but this can be changed using "hash-type".
\item[hdr(<name>)] The HTTP header <name> will be looked up in each HTTP
request. Just as with the equivalent ACL 'hdr()' function,
the header name in parenthesis is not case sensitive. If the
header is absent or if it does not contain any value, the
roundrobin algorithm is applied instead.
An optional 'use\_domain\_only' parameter is available, for
reducing the hash algorithm to the main domain part with some
specific headers such as 'Host'. For instance, in the Host
value "haproxy.1wt.eu", only "1wt" will be considered.
This algorithm is static by default, which means that
changing a server's weight on the fly will have no effect,
but this can be changed using "hash-type".
\item[rdp-cookie(<name>)]
The RDP cookie <name> (or "mstshash" if omitted) will be
looked up and hashed for each incoming TCP request. Just as
with the equivalent ACL 'req\_rdp\_cookie()' function, the name
is not case-sensitive. This mechanism is useful as a degraded
persistence mode, as it makes it possible to always send the
same user (or the same session ID) to the same server. If the
cookie is not found, the normal roundrobin algorithm is
used instead.
Note that for this to work, the frontend must ensure that an
RDP cookie is already present in the request buffer. For this
you must use 'tcp-request content accept' rule combined with
a 'req\_rdp\_cookie\_cnt' ACL.
This algorithm is static by default, which means that
changing a server's weight on the fly will have no effect,
but this can be changed using "hash-type".
See also the rdp\_cookie pattern fetch function.
\end{description}
\paragraph*{<arguments>}
is an optional list of arguments which may be needed by some
algorithms. Right now, only "url\_param" and "uri" support an
optional argument.
\begin{verbatim}
balance uri [len <len>] [depth <depth>]
balance url_param <param> [check_post [<max_wait>]]
\end{verbatim}
The load balancing algorithm of a backend is set to roundrobin when no other
algorithm, mode nor option have been set. The algorithm may only be set once
for each backend.
Examples:
\begin{verbatim}
balance roundrobin
balance url_param userid
balance url_param session_id check_post 64
balance hdr(User-Agent)
balance hdr(host)
balance hdr(Host) use_domain_only
\end{verbatim}
\emph{Note:} the following caveats and limitations on using the "check\_post"
extension with "url\_param" must be considered:
\begin{itemize}
\item[-] all POST requests are eligible for consideration, because there is no way
to determine if the parameters will be found in the body or entity which
may contain binary data. Therefore another method may be required to
restrict consideration of POST requests that have no URL parameters in
the body. (see acl reqideny http\_end)
\item[-] using a <max\_wait> value larger than the request buffer size does not
make sense and is useless. The buffer size is set at build time, and
defaults to 16 kB.
\item[-] Content-Encoding is not supported, the parameter search will probably
fail; and load balancing will fall back to Round Robin.
\item[-] Expect: 100-continue is not supported, load balancing will fall back to
Round Robin.
\item[-] Transfer-Encoding (RFC2616 3.6.1) is only supported in the first chunk.
If the entire parameter value is not present in the first chunk, the
selection of server is undefined (actually, defined by how little
actually appeared in the first chunk).
\item[-] This feature does not support generation of a 100, 411 or 501 response.
\item[-] In some cases, requesting "check\_post" MAY attempt to scan the entire
contents of a message body. Scanning normally terminates when linear
white space or control characters are found, indicating the end of what
might be a URL parameter list. This is probably not a concern with SGML
type message bodies.
\end{itemize}
See also: "dispatch", "cookie", "appsession", "transparent", "hash-type" and
"http\_proxy".
\subsubsection[bind]{bind [<address>]:<port\_range> [, ...]}
\subsubsection*{bind [<address>]:<port\_range> [, ...] interface <interface>}
\subsubsection*{bind [<address>]:<port\_range> [, ...] mss <maxseg>}
\subsubsection*{bind [<address>]:<port\_range> [, ...] transparent}
\subsubsection*{bind [<address>]:<port\_range> [, ...] id <id>}
\subsubsection*{bind [<address>]:<port\_range> [, ...] name <name>}
\subsubsection*{bind [<address>]:<port\_range> [, ...] defer-accept}
\subsubsection*{bind [<address>]:<port\_range> [, ...] accept-proxy}
\subsubsection*{bind /<path> [, ...]}
\subsubsection*{bind /<path> [, ...] mode <mode>}
\subsubsection*{bind /<path> [, ...] [ user <user> | uid <uid> ]}
\subsubsection*{bind /<path> [, ...] [ group <user> | gid <gid> ]}
\index{bind}
Define one or several listening addresses and/or ports in a frontend.
\dflb{no}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<address>] is optional and can be a host name, an IPv4 address, an IPv6
address, or '*'. It designates the address the frontend will
listen on. If unset, all IPv4 addresses of the system will be
listened on. The same will apply for '*' or the system's
special address "0.0.0.0". The IPv6 equivalent is '::'.
\item[<port\_range>] is either a unique TCP port, or a port range for which the
proxy will accept connections for the IP address specified
above. The port is mandatory for TCP listeners. Note that in
the case of an IPv6 address, the port is always the number
after the last colon ('\verb|:|'). A range can either be:
\begin{itemize}
\item[-] a numerical port (ex: '80')
\item[-] a dash-delimited ports range explicitly stating the lower
and upper bounds (ex: '2000-2100') which are included in
the range.
\end{itemize}
Particular care must be taken against port ranges, because
every <address:port> couple consumes one socket (= a file
descriptor), so it's easy to consume lots of descriptors
with a simple range, and to run out of sockets. Also, each
<address:port> couple must be used only once among all
instances running on a same system. Please note that binding
to ports lower than 1024 generally require particular
privileges to start the program, which are independant of
the 'uid' parameter.
\item[<path>] is a UNIX socket path beginning with a slash ('\verb|/|'). This is
alternative to the TCP listening port. Haproxy will then
receive UNIX connections on the socket located at this place.
The path must begin with a slash and by default is absolute.
It can be relative to the prefix defined by "unix-bind" in
the global section. Note that the total length of the prefix
followed by the socket path cannot exceed some system limits
for UNIX sockets, which commonly are set to 107 characters.
\item[<interface>] is an optional physical interface name. This is currently
only supported on Linux. The interface must be a physical
interface, not an aliased interface. When specified, all
addresses on the same line will only be accepted if the
incoming packet physically come through the designated
interface. It is also possible to bind multiple frontends to
the same address if they are bound to different interfaces.
Note that binding to a physical interface requires root
privileges. This parameter is only compatible with TCP
sockets.
\item[<maxseg>] is an optional TCP Maximum Segment Size (MSS) value to be
advertised on incoming connections. This can be used to force
a lower MSS for certain specific ports, for instance for
connections passing through a VPN. Note that this relies on a
kernel feature which is theorically supported under Linux but
was buggy in all versions prior to 2.6.28. It may or may not
work on other operating systems. It may also not change the
advertised value but change the effective size of outgoing
segments. The commonly advertised value on Ethernet networks
is 1460 = 1500(MTU) - 40(IP+TCP). If this value is positive,
it will be used as the advertised MSS. If it is negative, it
will indicate by how much to reduce the incoming connection's
advertised MSS for outgoing segments. This parameter is only
compatible with TCP sockets.
\item[<id>] is a persistent value for socket ID. Must be positive and
unique in the proxy. An unused value will automatically be
assigned if unset. Can only be used when defining only a
single socket.
\item[<name>] is an optional name provided for stats
\item[<mode>] is the octal mode used to define access permissions on the
UNIX socket. It can also be set by default in the global
section's "unix-bind" statement. Note that some platforms
simply ignore this.
\item[<user>] is the name of user that will be marked owner of the UNIX
socket. It can also be set by default in the global
section's "unix-bind" statement. Note that some platforms
simply ignore this.
\item[<group>] is the name of a group that will be used to create the UNIX
socket. It can also be set by default in the global section's
"unix-bind" statement. Note that some platforms simply ignore
this.
\item[<uid>] is the uid of user that will be marked owner of the UNIX
socket. It can also be set by default in the global section's
"unix-bind" statement. Note that some platforms simply ignore
this.
\item[<gid>] is the gid of a group that will be used to create the UNIX
socket. It can also be set by default in the global section's
"unix-bind" statement. Note that some platforms simply ignore
this.
\item[transparent] is an optional keyword which is supported only on certain
Linux kernels. It indicates that the addresses will be bound
even if they do not belong to the local machine. Any packet
targeting any of these addresses will be caught just as if
the address was locally configured. This normally requires
that IP forwarding is enabled. Caution! do not use this with
the default address '*', as it would redirect any traffic for
the specified port. This keyword is available only when
HAProxy is built with USE\_LINUX\_TPROXY=1. This parameter is
only compatible with TCP sockets.
\item[defer-accept] is an optional keyword which is supported only on certain
Linux kernels. It states that a connection will only be
accepted once some data arrive on it, or at worst after the
first retransmit. This should be used only on protocols for
which the client talks first (eg: HTTP). It can slightly
improve performance by ensuring that most of the request is
already available when the connection is accepted. On the
other hand, it will not be able to detect connections which
don't talk. It is important to note that this option is
broken in all kernels up to 2.6.31, as the connection is
never accepted until the client talks. This can cause issues
with front firewalls which would see an established
connection while the proxy will only see it in SYN\_RECV.
\item[accept-proxy] is an optional keyword which enforces use of the PROXY
protocol over any connection accepted by this listener. The
PROXY protocol dictates the layer 3/4 addresses of the
incoming connection to be used everywhere an address is used,
with the only exception of "tcp-request connection" rules
which will only see the real connection address. Logs will
reflect the addresses indicated in the protocol, unless it is
violated, in which case the real address will still be used.
This keyword combined with support from external components
can be used as an efficient and reliable alternative to the
X-Forwarded-For mechanism which is not always reliable and
not even always usable.
\end{description}
It is possible to specify a list of address:port combinations delimited by
commas. The frontend will then listen on all of these addresses. There is no
fixed limit to the number of addresses and ports which can be listened on in
a frontend, as well as there is no limit to the number of "bind" statements
in a frontend.
Example:
\begin{verbatim}
listen http_proxy
bind :80,:443
bind 10.0.0.1:10080,10.0.0.1:10443
bind /var/run/ssl-frontend.sock user root mode 600 accept-proxy
\end{verbatim}
See also: "source", "option forwardfor", "unix-bind" and the PROXY protocol
documentation.
\subsubsection[bind-process]{bind-process [ all | odd | even | <number 1-32> ] ...}
\index{bind-process}
Limit visibility of an instance to a certain set of processes numbers.
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[all] All process will see this instance. This is the default. It
may be used to override a default value.
\item[odd] This instance will be enabled on processes 1,3,5,...31. This
option may be combined with other numbers.
\item[even] This instance will be enabled on processes 2,4,6,...32. This
option may be combined with other numbers. Do not use it
with less than 2 processes otherwise some instances might be
missing from all processes.
\item[number] The instance will be enabled on this process number, between
1 and 32. You must be careful not to reference a process
number greater than the configured global.nbproc, otherwise
some instances might be missing from all processes.
\end{description}
This keyword limits binding of certain instances to certain processes. This
is useful in order not to have too many processes listening to the same
ports. For instance, on a dual-core machine, it might make sense to set
'nbproc 2' in the global section, then distributes the listeners among 'odd'
and 'even' instances.
At the moment, it is not possible to reference more than 32 processes using
this keyword, but this should be more than enough for most setups. Please
note that 'all' really means all processes and is not limited to the first
32.
If some backends are referenced by frontends bound to other processes, the
backend automatically inherits the frontend's processes.
Example:
\begin{verbatim}
listen app_ip1
bind 10.0.0.1:80
bind-process odd
listen app_ip2
bind 10.0.0.2:80
bind-process even
listen management
bind 10.0.0.3:80
bind-process 1 2 3 4
\end{verbatim}
See also: "nbproc" in global section.
\subsubsection[block]{block { if | unless } <condition>}
\index{block}
Block a layer 7 request if/unless a condition is matched
\dflb{no}{yes}{yes}{yes}
The HTTP request will be blocked very early in the layer 7 processing
if/unless <condition> is matched. A 403 error will be returned if the request
is blocked. The condition has to reference ACLs (see section 7). This is
typically used to deny access to certain sensitive resources if some
conditions are met or not met. There is no fixed limit to the number of
"block" statements per instance.
Example:
\begin{verbatim}
acl invalid_src src 0.0.0.0/7 224.0.0.0/3
acl invalid_src src_port 0:1023
acl local_dst hdr(host) -i localhost
block if invalid_src || local_dst
\end{verbatim}
See section 7 about ACL usage.
\subsubsection[capture cookie]{capture cookie <name> len <length>}
Capture and log a cookie in the request and in the response.
\dflb{no}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<name>] is the beginning of the name of the cookie to capture. In order
to match the exact name, simply suffix the name with an equal
sign ('\verb|=|'). The full name will appear in the logs, which is
useful with application servers which adjust both the cookie name
and value (eg: ASPSESSIONXXXXX).
\item[<length>] is the maximum number of characters to report in the logs, which
include the cookie name, the equal sign and the value, all in the
standard "name=value" form. The string will be truncated on the
right if it exceeds <length>.
\end{description}
Only the first cookie is captured. Both the "cookie" request headers and the
"set-cookie" response headers are monitored. This is particularly useful to
check for application bugs causing session crossing or stealing between
users, because generally the user's cookies can only change on a login page.
When the cookie was not presented by the client, the associated log column
will report "-". When a request does not cause a cookie to be assigned by the
server, a "-" is reported in the response column.
The capture is performed in the frontend only because it is necessary that
the log format does not change for a given frontend depending on the
backends. This may change in the future. Note that there can be only one
"capture cookie" statement in a frontend. The maximum capture length is
configured in the sources by default to 64 characters. It is not possible to
specify a capture in a "defaults" section.
Example:
\verb|capture cookie ASPSESSION len 32|
See also: "capture request header", "capture response header" as well as
section 8 about logging.
\subsubsection[capture request header]{capture request header <name> len <length>}
\index{capture request header}
Capture and log the first occurrence of the specified request header.
\dflb{no}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<name>] is the name of the header to capture. The header names are not
case-sensitive, but it is a common practice to write them as they
appear in the requests, with the first letter of each word in
upper case. The header name will not appear in the logs, only the
value is reported, but the position in the logs is respected.
\item[<length>] is the maximum number of characters to extract from the value and
report in the logs. The string will be truncated on the right if
it exceeds <length>.
\end{description}
Only the first value of the last occurrence of the header is captured. The
value will be added to the logs between braces ('\verb|{}|'). If multiple headers
are captured, they will be delimited by a vertical bar ('\verb:|:') and will appear
in the same order they were declared in the configuration. Non-existent
headers will be logged just as an empty string. Common uses for request
header captures include the "Host" field in virtual hosting environments, the
"Content-length" when uploads are supported, "User-agent" to quickly
differentiate between real users and robots, and "X-Forwarded-For" in proxied
environments to find where the request came from.
Note that when capturing headers such as "User-agent", some spaces may be
logged, making the log analysis more difficult. Thus be careful about what
you log if you know your log parser is not smart enough to rely on the
braces.
There is no limit to the number of captured request headers, but each capture
is limited to 64 characters. In order to keep log format consistent for a
same frontend, header captures can only be declared in a frontend. It is not
possible to specify a capture in a "defaults" section.
Example:
\begin{verbatim}
capture request header Host len 15
capture request header X-Forwarded-For len 15
capture request header Referrer len 15
\end{verbatim}
See also: "capture cookie", "capture response header" as well as section 8
about logging.
\subsubsection[capture response header]{capture response header <name> len <length>}
\index{capture response header}
Capture and log the first occurrence of the specified response header.
\dflb{no}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<name>] is the name of the header to capture. The header names are not
case-sensitive, but it is a common practice to write them as they
appear in the response, with the first letter of each word in
upper case. The header name will not appear in the logs, only the
value is reported, but the position in the logs is respected.
\item[<length>] is the maximum number of characters to extract from the value and
report in the logs. The string will be truncated on the right if
it exceeds <length>.
\end{description}
Only the first value of the last occurrence of the header is captured. The
result will be added to the logs between braces ('\verb|{}|') after the captured
request headers. If multiple headers are captured, they will be delimited by
a vertical bar ('\verb:|:') and will appear in the same order they were declared in
the configuration. Non-existent headers will be logged just as an empty
string. Common uses for response header captures include the "Content-length"
header which indicates how many bytes are expected to be returned, the
"Location" header to track redirections.
There is no limit to the number of captured response headers, but each
capture is limited to 64 characters. In order to keep log format consistent
for a same frontend, header captures can only be declared in a frontend. It
is not possible to specify a capture in a "defaults" section.
Example:
\begin{verbatim}
capture response header Content-length len 9
capture response header Location len 15
\end{verbatim}
See also: "capture cookie", "capture request header" as well as section 8
about logging.
\subsubsection[clitimeout]{clitimeout <timeout> (deprecated)}
\index{clitimeout}
Set the maximum inactivity time on the client side.
\dflb{yes}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<timeout>] is the timeout value is specified in milliseconds by default, but
can be in any other unit if the number is suffixed by the unit,
as explained at the top of this document.
\end{description}
The inactivity timeout applies when the client is expected to acknowledge or
send data. In HTTP mode, this timeout is particularly important to consider
during the first phase, when the client sends the request, and during the
response while it is reading data sent by the server. The value is specified
in milliseconds by default, but can be in any other unit if the number is
suffixed by the unit, as specified at the top of this document. In TCP mode
(and to a lesser extent, in HTTP mode), it is highly recommended that the
client timeout remains equal to the server timeout in order to avoid complex
situations to debug. It is a good practice to cover one or several TCP packet
losses by specifying timeouts that are slightly above multiples of 3 seconds
(eg: 4 or 5 seconds).
This parameter is specific to frontends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of expired sessions in
the system if the system's timeouts are not configured either.
This parameter is provided for compatibility but is currently deprecated.
Please use "timeout client" instead.
See also: "timeout client", "timeout http-request", "timeout server", and
"srvtimeout".
\subsubsection[contimeout]{contimeout <timeout> (deprecated)}
\index{contimeout}
Set the maximum time to wait for a connection attempt to a server to succeed.
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<timeout>] is the timeout value is specified in milliseconds by default, but
can be in any other unit if the number is suffixed by the unit,
as explained at the top of this document.
\end{description}
If the server is located on the same LAN as haproxy, the connection should be
immediate (less than a few milliseconds). Anyway, it is a good practice to
cover one or several TCP packet losses by specifying timeouts that are
slightly above multiples of 3 seconds (eg: 4 or 5 seconds). By default, the
connect timeout also presets the queue timeout to the same value if this one
has not been specified. Historically, the contimeout was also used to set the
tarpit timeout in a listen section, which is not possible in a pure frontend.
This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of failed sessions in
the system if the system's timeouts are not configured either.
This parameter is provided for backwards compatibility but is currently
deprecated. Please use "timeout connect", "timeout queue" or "timeout tarpit"
instead.
See also: "timeout connect", "timeout queue", "timeout tarpit",
"timeout server", "contimeout".
\subsubsection[cookie]{cookie <name> [ rewrite | insert | prefix ] [ indirect ] [ nocache ] [ postonly ] [ preserve ] [ httponly ] [ secure ] [ domain <domain> ]* [ maxidle <idle> ] [ maxlife <life> ]}
\index{cookie}
Enable cookie-based persistence in a backend.
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<name>] is the name of the cookie which will be monitored, modified or
inserted in order to bring persistence. This cookie is sent to
the client via a "Set-Cookie" header in the response, and is
brought back by the client in a "Cookie" header in all requests.
Special care should be taken to choose a name which does not
conflict with any likely application cookie. Also, if the same
backends are subject to be used by the same clients (eg:
HTTP/HTTPS), care should be taken to use different cookie names
between all backends if persistence between them is not desired.
\item[rewrite] This keyword indicates that the cookie will be provided by the
server and that haproxy will have to modify its value to set the
server's identifier in it. This mode is handy when the management
of complex combinations of "Set-cookie" and "Cache-control"
headers is left to the application. The application can then
decide whether or not it is appropriate to emit a persistence
cookie. Since all responses should be monitored, this mode only
works in HTTP close mode. Unless the application behaviour is
very complex and/or broken, it is advised not to start with this
mode for new deployments. This keyword is incompatible with
"insert" and "prefix".
\item[insert] This keyword indicates that the persistence cookie will have to
be inserted by haproxy in server responses if the client did not
already have a cookie that would have permitted it to access this
server. When used without the "preserve" option, if the server
emits a cookie with the same name, it will be remove before
processing. For this reason, this mode can be used to upgrade
existing configurations running in the "rewrite" mode. The cookie
will only be a session cookie and will not be stored on the
client's disk. By default, unless the "indirect" option is added,
the server will see the cookies emitted by the client. Due to
caching effects, it is generally wise to add the "nocache" or
"postonly" keywords (see below). The "insert" keyword is not
compatible with "rewrite" and "prefix".
\item[prefix] This keyword indicates that instead of relying on a dedicated
cookie for the persistence, an existing one will be completed.
This may be needed in some specific environments where the client
does not support more than one single cookie and the application
already needs it. In this case, whenever the server sets a cookie
named <name>, it will be prefixed with the server's identifier
and a delimiter. The prefix will be removed from all client
requests so that the server still finds the cookie it emitted.
Since all requests and responses are subject to being modified,
this mode requires the HTTP close mode. The "prefix" keyword is
not compatible with "rewrite" and "insert". Note: it is highly
recommended not to use "indirect" with "prefix", otherwise server
cookie updates would not be sent to clients.
\item[indirect] When this option is specified, no cookie will be emitted to a
client which already has a valid one for the server which has
processed the request. If the server sets such a cookie itself,
it will be removed, unless the "preserve" option is also set. In
"insert" mode, this will additionally remove cookies from the
requests transmitted to the server, making the persistence
mechanism totally transparent from an application point of view.
Note: it is highly recommended not to use "indirect" with
"prefix", otherwise server cookie updates would not be sent to
clients.
\item[nocache] This option is recommended in conjunction with the insert mode
when there is a cache between the client and HAProxy, as it
ensures that a cacheable response will be tagged non-cacheable if
a cookie needs to be inserted. This is important because if all
persistence cookies are added on a cacheable home page for
instance, then all customers will then fetch the page from an
outer cache and will all share the same persistence cookie,
leading to one server receiving much more traffic than others.
See also the "insert" and "postonly" options.
\item[postonly] This option ensures that cookie insertion will only be performed
on responses to POST requests. It is an alternative to the
"nocache" option, because POST responses are not cacheable, so
this ensures that the persistence cookie will never get cached.
Since most sites do not need any sort of persistence before the
first POST which generally is a login request, this is a very
efficient method to optimize caching without risking to find a
persistence cookie in the cache.
See also the "insert" and "nocache" options.
\item[preserve] This option may only be used with "insert" and/or "indirect". It
allows the server to emit the persistence cookie itself. In this
case, if a cookie is found in the response, haproxy will leave it
untouched. This is useful in order to end persistence after a
logout request for instance. For this, the server just has to
emit a cookie with an invalid value (eg: empty) or with a date in
the past. By combining this mechanism with the "disable-on-404"
check option, it is possible to perform a completely graceful
shutdown because users will definitely leave the server after
they logout.
\item[httponly] This option tells haproxy to add an "HttpOnly" cookie attribute
when a cookie is inserted. This attribute is used so that a
user agent doesn't share the cookie with non-HTTP components.
Please check RFC6265 for more information on this attribute.
\item[secure] This option tells haproxy to add a "Secure" cookie attribute when
a cookie is inserted. This attribute is used so that a user agent
never emits this cookie over non-secure channels, which means
that a cookie learned with this flag will be presented only over
SSL/TLS connections. Please check RFC6265 for more information on
this attribute.
\item[domain] This option allows to specify the domain at which a cookie is
inserted. It requires exactly one parameter: a valid domain
name. If the domain begins with a dot, the browser is allowed to
use it for any host ending with that name. It is also possible to
specify several domain names by invoking this option multiple
times. Some browsers might have small limits on the number of
domains, so be careful when doing that. For the record, sending
10 domains to MSIE 6 or Firefox 2 works as expected.
\item[maxidle] This option allows inserted cookies to be ignored after some idle
time. It only works with insert-mode cookies. When a cookie is
sent to the client, the date this cookie was emitted is sent too.
Upon further presentations of this cookie, if the date is older
than the delay indicated by the parameter (in seconds), it will
be ignored. Otherwise, it will be refreshed if needed when the
response is sent to the client. This is particularly useful to
prevent users who never close their browsers from remaining for
too long on the same server (eg: after a farm size change). When
this option is set and a cookie has no date, it is always
accepted, but gets refreshed in the response. This maintains the
ability for admins to access their sites. Cookies that have a
date in the future further than 24 hours are ignored. Doing so
lets admins fix timezone issues without risking kicking users off
the site.
\item[maxlife] This option allows inserted cookies to be ignored after some life
time, whether they're in use or not. It only works with insert
mode cookies. When a cookie is first sent to the client, the date
this cookie was emitted is sent too. Upon further presentations
of this cookie, if the date is older than the delay indicated by
the parameter (in seconds), it will be ignored. If the cookie in
the request has no date, it is accepted and a date will be set.
Cookies that have a date in the future further than 24 hours are
ignored. Doing so lets admins fix timezone issues without risking
kicking users off the site. Contrary to maxidle, this value is
not refreshed, only the first visit date counts. Both maxidle and
maxlife may be used at the time. This is particularly useful to
prevent users who never close their browsers from remaining for
too long on the same server (eg: after a farm size change). This
is stronger than the maxidle method in that it forces a
redispatch after some absolute delay.
\end{description}
There can be only one persistence cookie per HTTP backend, and it can be
declared in a defaults section. The value of the cookie will be the value
indicated after the "cookie" keyword in a "server" statement. If no cookie
is declared for a given server, the cookie is not set.
Examples:
\begin{verbatim}
cookie JSESSIONID prefix
cookie SRV insert indirect nocache
cookie SRV insert postonly indirect
cookie SRV insert indirect nocache maxidle 30m maxlife 8h
\end{verbatim}
See also: "appsession", "balance source", "capture cookie", "server"
and "ignore-persist".
\subsubsection[default-server]{default-server [param*]}
\index{default-server}
Change default options for a server in a backend
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<param*>] is a list of parameters for this server. The "default-server"
keyword accepts an important number of options and has a complete
section dedicated to it. Please refer to section 5 for more
details.
\end{description}
Example:
\begin{verbatim}
default-server inter 1000 weight 13
\end{verbatim}
See also: "server" and section 5 about server options
\subsubsection[default\_backend]{default\_backend <backend>}
\index{default\_backend}
Specify the backend to use when no "use\_backend" rule has been matched.
\dflb{yes}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<backend>] is the name of the backend to use.
\end{description}
When doing content-switching between frontend and backends using the
"use\_backend" keyword, it is often useful to indicate which backend will be
used when no rule has matched. It generally is the dynamic backend which
will catch all undetermined requests.
Example:
\begin{verbatim}
use_backend dynamic if url_dyn
use_backend static if url_css url_img extension_img
default_backend dynamic
\end{verbatim}
See also: "use\_backend", "reqsetbe", "reqisetbe"
\subsubsection[disabled]{disabled}
\index{disabled}
Disable a proxy, frontend or backend.
\dflb{yes}{yes}{yes}{yes}
Arguments: none
The "disabled" keyword is used to disable an instance, mainly in order to
liberate a listening port or to temporarily disable a service. The instance
will still be created and its configuration will be checked, but it will be
created in the "stopped" state and will appear as such in the statistics. It
will not receive any traffic nor will it send any health-checks or logs. It
is possible to disable many instances at once by adding the "disabled"
keyword in a "defaults" section.
See also: "enabled"
\subsubsection[dispatch]{dispatch <address>:<port>}
\index{dispatch}
Set a default server address
\dflb{no}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<address>] is the IPv4 address of the default server. Alternatively, a
resolvable hostname is supported, but this name will be resolved
during start-up.
\item[<ports>] is a mandatory port specification. All connections will be sent
to this port, and it is not permitted to use port offsets as is
possible with normal servers.
\end{description}
The "dispatch" keyword designates a default server for use when no other
server can take the connection. In the past it was used to forward non
persistent connections to an auxiliary load balancer. Due to its simple
syntax, it has also been used for simple TCP relays. It is recommended not to
use it for more clarity, and to use the "server" directive instead.
See also: "server"
\subsubsection[enabled]{enabled}
\index{enabled}
Enable a proxy, frontend or backend.
\dflb{yes}{yes}{yes}{yes}
Arguments: none
The "enabled" keyword is used to explicitly enable an instance, when the
defaults has been set to "disabled". This is very rarely used.
See also: "disabled"
\subsubsection[errorfile]{errorfile <code> <file>}
\index{errorfile}
Return a file contents instead of errors generated by HAProxy
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<code>] is the HTTP status code. Currently, HAProxy is capable of
generating codes 200, 400, 403, 408, 500, 502, 503, and 504.
\item[<file>] designates a file containing the full HTTP response. It is
recommended to follow the common practice of appending ".http" to
the filename so that people do not confuse the response with HTML
error pages, and to use absolute paths, since files are read
before any chroot is performed.
\end{description}
It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.
Code 200 is emitted in response to requests matching a "monitor-uri" rule.
The files are returned verbatim on the TCP socket. This allows any trick such
as redirections to another URL or site, as well as tricks to clean cookies,
force enable or disable caching, etc... The package provides default error
files returning the same contents as default errors.
The files should not exceed the configured buffer size (BUFSIZE), which
generally is 8 or 16 kB, otherwise they will be truncated. It is also wise
not to put any reference to local contents (eg: images) in order to avoid
loops between the client and HAProxy when all servers are down, causing an
error to be returned instead of an image. For better HTTP compliance, it is
recommended that all header lines end with CR-LF and not LF alone.
The files are read at the same time as the configuration and kept in memory.
For this reason, the errors continue to be returned even when the process is
chrooted, and no file change is considered while the process is running. A
simple method for developing those files consists in associating them to the
403 status code and interrogating a blocked URL.
See also: "errorloc", "errorloc302", "errorloc303"
Example:
\begin{verbatim}
errorfile 400 /etc/haproxy/errorfiles/400badreq.http
errorfile 403 /etc/haproxy/errorfiles/403forbid.http
errorfile 503 /etc/haproxy/errorfiles/503sorry.http
\end{verbatim}
\subsubsection[errorloc]{errorloc <code> <url>}
\subsubsection[errorloc302]{errorloc302 <code> <url>}
\index{errorloc}
\index{errorloc302}
Return an HTTP redirection to a URL instead of errors generated by HAProxy
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<code>] is the HTTP status code. Currently, HAProxy is capable of
generating codes 200, 400, 403, 408, 500, 502, 503, and 504.
\item[<url>] it is the exact contents of the "Location" header. It may contain
either a relative URI to an error page hosted on the same site,
or an absolute URI designating an error page on another site.
Special care should be given to relative URIs to avoid redirect
loops if the URI itself may generate the same error (eg: 500).
\end{description}
It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.
Code 200 is emitted in response to requests matching a "monitor-uri" rule.
Note that both keyword return the HTTP 302 status code, which tells the
client to fetch the designated URL using the same HTTP method. This can be
quite problematic in case of non-GET methods such as POST, because the URL
sent to the client might not be allowed for something other than GET. To
workaround this problem, please use "errorloc303" which send the HTTP 303
status code, indicating to the client that the URL must be fetched with a GET
request.
See also: "errorfile", "errorloc303"
\subsubsection[errorloc303]{errorloc303 <code> <url>}
\index{errorloc303}
Return an HTTP redirection to a URL instead of errors generated by HAProxy
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<code>] is the HTTP status code. Currently, HAProxy is capable of
generating codes 400, 403, 408, 500, 502, 503, and 504.
\item[<url>] it is the exact contents of the "Location" header. It may contain
either a relative URI to an error page hosted on the same site,
or an absolute URI designating an error page on another site.
Special care should be given to relative URIs to avoid redirect
loops if the URI itself may generate the same error (eg: 500).
\end{description}
It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.
Code 200 is emitted in response to requests matching a "monitor-uri" rule.
Note that both keyword return the HTTP 303 status code, which tells the
client to fetch the designated URL using the same HTTP GET method. This
solves the usual problems associated with "errorloc" and the 302 code. It is
possible that some very old browsers designed before HTTP/1.1 do not support
it, but no such problem has been reported till now.
See also: "errorfile", "errorloc", "errorloc302"
\subsubsection[force-persist]{force-persist { if | unless } <condition>}
\index{force-persist}
Declare a condition to force persistence on down servers
\dflb{no}{yes}{yes}{yes}
By default, requests are not dispatched to down servers. It is possible to
force this using "option persist", but it is unconditional and redispatches
to a valid server if "option redispatch" is set. That leaves with very little
possibilities to force some requests to reach a server which is artificially
marked down for maintenance operations.
The "force-persist" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore the down status of
a server and still try to connect to it. That makes it possible to start a
server, still replying an error to the health checks, and run a specially
configured browser to test the service. Among the handy methods, one could
use a specific source IP address, or a specific cookie. The cookie also has
the advantage that it can easily be added/removed on the browser from a test
page. Once the service is validated, it is then possible to open the service
to the world by returning a valid response to health checks.
The forced persistence is enabled when an "if" condition is met, or unless an
"unless" condition is met. The final redispatch is always disabled when this
is used.
See also: "option redispatch", "ignore-persist", "persist",
and section 7 about ACL usage.
\subsubsection[fullconn]{fullconn <conns>}
\index{fullconn}
Specify at what backend load the servers will reach their maxconn
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<conns>] is the number of connections on the backend which will make the
servers use the maximal number of connections.
\end{description}
When a server has a "maxconn" parameter specified, it means that its number
of concurrent connections will never go higher. Additionally, if it has a
"minconn" parameter, it indicates a dynamic limit following the backend's
load. The server will then always accept at least <minconn> connections,
never more than <maxconn>, and the limit will be on the ramp between both
values when the backend has less than <conns> concurrent connections. This
makes it possible to limit the load on the servers during normal loads, but
push it further for important loads without overloading the servers during
exceptional loads.
Since it's hard to get this value right, haproxy automatically sets it to
10\% of the sum of the maxconns of all frontends that may branch to this
backend. That way it's safe to leave it unset.
Example:
\begin{verbatim}
# The servers will accept between 100 and 1000 concurrent connections each
# and the maximum of 1000 will be reached when the backend reaches 10000
# connections.
backend dynamic
fullconn 10000
server srv1 dyn1:80 minconn 100 maxconn 1000
server srv2 dyn2:80 minconn 100 maxconn 1000
\end{verbatim}
See also: "maxconn", "server"
\subsubsection[grace]{grace <time>}
\index{grace}
Maintain a proxy operational for some time after a soft stop
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<time>] is the time (by default in milliseconds) for which the instance
will remain operational with the frontend sockets still listening
when a soft-stop is received via the SIGUSR1 signal.
\end{description}
This may be used to ensure that the services disappear in a certain order.
This was designed so that frontends which are dedicated to monitoring by an
external equipment fail immediately while other ones remain up for the time
needed by the equipment to detect the failure.
Note that currently, there is very little benefit in using this parameter,
and it may in fact complicate the soft-reconfiguration process more than
simplify it.
\subsubsection[hash-type]{hash-type <method>}
\index{hash-type}
Specify a method to use for mapping hashes to servers
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[map-based] the hash table is a static array containing all alive servers.
The hashes will be very smooth, will consider weights, but will
be static in that weight changes while a server is up will be
ignored. This means that there will be no slow start. Also,
since a server is selected by its position in the array, most
mappings are changed when the server count changes. This means
that when a server goes up or down, or when a server is added
to a farm, most connections will be redistributed to different
servers. This can be inconvenient with caches for instance.
\item[avalanche] this mechanism uses the default map-based hashing described
above but applies a full avalanche hash before performing the
mapping. The result is a slightly less smooth hash for most
situations, but the hash becomes better than pure map-based
hashes when the number of servers is a multiple of the size of
the input set. When using URI hash with a number of servers
multiple of 64, it's desirable to change the hash type to
this value.
\item[consistent] the hash table is a tree filled with many occurrences of each
server. The hash key is looked up in the tree and the closest
server is chosen. This hash is dynamic, it supports changing
weights while the servers are up, so it is compatible with the
slow start feature. It has the advantage that when a server
goes up or down, only its associations are moved. When a server
is added to the farm, only a few part of the mappings are
redistributed, making it an ideal algorithm for caches.
However, due to its principle, the algorithm will never be very
smooth and it may sometimes be necessary to adjust a server's
weight or its ID to get a more balanced distribution. In order
to get the same distribution on multiple load balancers, it is
important that all servers have the same IDs.
\end{description}
The default hash type is "map-based" and is recommended for most usages.
See also: "balance", "server"
\subsubsection[http-check disable-on-404]{http-check disable-on-404}
\index{http-check disable-on-404}
Enable a maintenance mode upon HTTP/404 response to health-checks
\dflb{yes}{no}{yes}{yes}
Arguments: none
When this option is set, a server which returns an HTTP code 404 will be
excluded from further load-balancing, but will still receive persistent
connections. This provides a very convenient method for Web administrators
to perform a graceful shutdown of their servers. It is also important to note
that a server which is detected as failed while it was in this mode will not
generate an alert, just a notice. If the server responds 2xx or 3xx again, it
will immediately be reinserted into the farm. The status on the stats page
reports "NOLB" for a server in this mode. It is important to note that this
option only works in conjunction with the "httpchk" option. If this option
is used with "http-check expect", then it has precedence over it so that 404
responses will still be considered as soft-stop.
See also : "option httpchk", "http-check expect"
\subsubsection[http-check expect]{http-check expect [!] <match> <pattern>}
\index{http-check expect}
Make HTTP health checks consider response contents or specific status codes
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<match>] is a keyword indicating how to look for a specific pattern in the
response. The keyword may be one of "status", "rstatus",
"string", or "rstring". The keyword may be preceded by an
exclamation mark ('\verb|!|') to negate the match. Spaces are allowed
between the exclamation mark and the keyword. See below for more
details on the supported keywords.
\item[<pattern>] is the pattern to look for. It may be a string or a regular
expression. If the pattern contains spaces, they must be escaped
with the usual backslash ('\verb|\|').
\end{description}
By default, "option httpchk" considers that response statuses 2xx and 3xx
are valid, and that others are invalid. When "http-check expect" is used,
it defines what is considered valid or invalid. Only one "http-check"
statement is supported in a backend. If a server fails to respond or times
out, the check obviously fails.
The available matches are:
\begin{description}
\item[status <string>] test the exact string match for the HTTP status code.
A health check respose will be considered valid if the
response's status code is exactly this string. If the
"status" keyword is prefixed with "!", then the response
will be considered invalid if the status code matches.
\item[rstatus <regex>] test a regular expression for the HTTP status code.
A health check respose will be considered valid if the
response's status code matches the expression. If the
"rstatus" keyword is prefixed with "!", then the response
will be considered invalid if the status code matches.
This is mostly used to check for multiple codes.
\item[string <string>] test the exact string match in the HTTP response body.
A health check respose will be considered valid if the
response's body contains this exact string. If the
"string" keyword is prefixed with "!", then the response
will be considered invalid if the body contains this
string. This can be used to look for a mandatory word at
the end of a dynamic page, or to detect a failure when a
specific error appears on the check page (eg: a stack
trace).
\item[rstring <regex>] test a regular expression on the HTTP response body.
A health check respose will be considered valid if the
response's body matches this expression. If the "rstring"
keyword is prefixed with "!", then the response will be
considered invalid if the body matches the expression.
This can be used to look for a mandatory word at the end
of a dynamic page, or to detect a failure when a specific
error appears on the check page (eg: a stack trace).
\end{description}
It is important to note that the responses will be limited to a certain size
defined by the global "tune.chksize" option, which defaults to 16384 bytes.
Thus, too large responses may not contain the mandatory pattern when using
"string" or "rstring". If a large response is absolutely required, it is
possible to change the default max size by setting the global variable.
However, it is worth keeping in mind that parsing very large responses can
waste some CPU cycles, especially when regular expressions are used, and that
it is always better to focus the checks on smaller resources.
Last, if "http-check expect" is combined with "http-check disable-on-404",
then this last one has precedence when the server responds with 404.
Examples:
\begin{verbatim}
# only accept status 200 as valid
http-check expect status 200
# consider SQL errors as errors
http-check expect ! string SQL\ Error
# consider status 5xx only as errors
http-check expect ! rstatus ^5
# check that we have a correct hexadecimal tag before /html
http-check expect rstring <!--tag:[0-9a-f]*</html>
\end{verbatim}
See also: "option httpchk", "http-check disable-on-404"
\subsubsection[http-check send-state]{http-check send-state}
\index{http-check send-state}
Enable emission of a state header with HTTP health checks
\dflb{yes}{no}{yes}{yes}
Arguments: none
When this option is set, haproxy will systematically send a special header
"X-Haproxy-Server-State" with a list of parameters indicating to each server
how they are seen by haproxy. This can be used for instance when a server is
manipulated without access to haproxy and the operator needs to know whether
haproxy still sees it up or not, or if the server is the last one in a farm.
The header is composed of fields delimited by semi-colons, the first of which
is a word ("UP", "DOWN", "NOLB"), possibly followed by a number of valid
checks on the total number before transition, just as appears in the stats
interface. Next headers are in the form "<variable>=<value>", indicating in
no specific order some values available in the stats interface:
\begin{itemize}
\item[-] a variable "name", containing the name of the backend followed by a slash
(\verb|/|) then the name of the server. This can be used when a server is
checked in multiple backends.
\item[-] a variable "node" containing the name of the haproxy node, as set in the
global "node" variable, otherwise the system's hostname if unspecified.
\item[-] a variable "weight" indicating the weight of the server, a slash (\verb|/|)
and the total weight of the farm (just counting usable servers). This
helps to know if other servers are available to handle the load when this
one fails.
\item[-] a variable "scur" indicating the current number of concurrent connections
on the server, followed by a slash (\verb|/|) then the total number of
connections on all servers of the same backend.
\item[-] a variable "qcur" indicating the current number of requests in the
server's queue.
\end{itemize}
Example of a header received by the application server:
\begin{verbatim}
>>> X-Haproxy-Server-State: UP 2/3; name=bck/srv2; node=lb1; weight=1/2; \
scur=13/22; qcur=0
\end{verbatim}
See also: "option httpchk", "http-check disable-on-404"
\subsubsection[http-request]{http-request \{ allow | deny | auth [realm <realm>] \} [ \{ if | unless \} <condition> ]}
\index{http-request}
Access control for Layer 7 requests
\dflb{no}{yes}{yes}{yes}
These set of options allow to fine control access to a
frontend/listen/backend. Each option may be followed by if/unless and acl.
First option with matched condition (or option without condition) is final.
For "deny" a 403 error will be returned, for "allow" normal processing is
performed, for "auth" a 401/407 error code is returned so the client
should be asked to enter a username and password.
There is no fixed limit to the number of http-request statements per
instance.
Example:
\begin{verbatim}
acl nagios src 192.168.129.3
acl local_net src 192.168.0.0/16
acl auth_ok http_auth(L1)
http-request allow if nagios
http-request allow if local_net auth_ok
http-request auth realm Gimme if local_net auth_ok
http-request deny
\end{verbatim}
Example:
\begin{verbatim}
acl auth_ok http_auth_group(L1) G1
http-request auth unless auth_ok
\end{verbatim}
See also : "stats http-request", section 3.4 about userlists and section 7
about ACL usage.
\subsubsection[http-send-name-header]{http-send-name-header [<header>]}
\index{http-send-name-header}
Add the server name to a request. Use the header string given by <header>
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[ <header>] The header string to use to send the server name
\end{description}
The "http-send-name-header" statement causes the name of the target
server to be added to the headers of an HTTP request. The name
is added with the header string proved.
See also : "server"
\subsubsection[id]{id <value>}
\index{id}
Set a persistent ID to a proxy.
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<id>] ID of proxy
\end{description}
Set a persistent ID for the proxy. This ID must be unique and positive.
An unused ID will automatically be assigned if unset. The first assigned
value will be 1. This ID is currently only returned in statistics.
\subsubsection[ignore-persist]{ignore-persist \{ if | unless \} <condition>}
\index{ignore-persist}
Declare a condition to ignore persistence
\dflb{no}{yes}{yes}{yes}
By default, when cookie persistence is enabled, every requests containing
the cookie are unconditionally persistent (assuming the target server is up
and running).
The "ignore-persist" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore persistence.
This is sometimes useful to load balance requests for static files, which
oftenly don't require persistence. This can also be used to fully disable
persistence for a specific User-Agent (for example, some web crawler bots).
Combined with "appsession", it can also help reduce HAProxy memory usage, as
the appsession table won't grow if persistence is ignored.
The persistence is ignored when an "if" condition is met, or unless an
"unless" condition is met.
See also: "force-persist", "cookie", and section 7 about ACL usage.
\subsubsection[log global]{log global}
\subsubsection[log]{log <address> <facility> [<level> [<minlevel>]]}
\subsubsection[no log]{no log}
\index{log global}
\index{log}
\index{no log}
Enable per-instance logging of events and traffic.
\dflb{yes}{yes}{yes}{yes}
Prefix:
\begin{description}
\item[no] should be used when the logger list must be flushed. For example,
if you don't want to inherit from the default logger list. This
prefix does not allow arguments.
\end{description}
Arguments:
\begin{description}
\item[global] should be used when the instance's logging parameters are the
same as the global ones. This is the most common usage. "global"
replaces <address>, <facility> and <level> with those of the log
entries found in the "global" section. Only one "log global"
statement may be used per instance, and this form takes no other
parameter.
\item[<address>] indicates where to send the logs. It takes the same format as
for the "global" section's logs, and can be one of:
\begin{itemize}
\item[-] An IPv4 address optionally followed by a colon ('\verb|:|') and a UDP
port. If no port is specified, 514 is used by default (the
standard syslog port).
\item[-] An IPv6 address followed by a colon ('\verb|:|') and optionally a UDP
port. If no port is specified, 514 is used by default (the
standard syslog port).
\item[-] A filesystem path to a UNIX domain socket, keeping in mind
considerations for chroot (be sure the path is accessible
inside the chroot) and uid/gid (be sure the path is
appropriately writeable).
\end{itemize}
\item[<facility>] must be one of the 24 standard syslog facilities:
\index{Log facility}
\vspace{5mm}
\textbf{
\begin{tabular}{llllllll}
kern & user & mail & daemon & auth & syslog & lpr & news \\
uucp & cron & auth2 & ftp & ntp & audit & alert & cron2 \\
local0 & local1 & local2 & local3 & local4 & local5 & local6 & local7
\end{tabular}
}
\vspace{5mm}
\item[<level>] is optional and can be specified to filter outgoing messages. By
default, all messages are sent. If a level is specified, only
messages with a severity at least as important as this level
will be sent. An optional minimum level can be specified. If it
is set, logs emitted with a more severe level than this one will
be capped to this level. This is used to avoid sending "emerg"
messages on all terminals on some default syslog configurations.
\index{Log level}
Eight levels are known:
\vspace{3mm}
\textbf {
\begin{tabular}{llllllll}
emerg & alert & crit & err & warning & notice & info & debug
\end{tabular}
}
\end{description}
It is important to keep in mind that it is the frontend which decides what to
log from a connection, and that in case of content switching, the log entries
from the backend will be ignored. Connections are logged at level "info".
However, backend log declaration define how and where servers status changes
will be logged. Level "notice" will be used to indicate a server going up,
"warning" will be used for termination signals and definitive service
termination, and "alert" will be used for when a server goes down.
\emph{Note:} According to RFC3164, messages are truncated to 1024 bytes before
being emitted.
Example:
\begin{verbatim}
log global
log 127.0.0.1:514 local0 notice # only send important events
log 127.0.0.1:514 local0 notice notice # same but limit output level
\end{verbatim}
\subsubsection[log-format]{log-format <string>}
\index{log-format}
Allows you to custom a log line.
See also: Custom Log Format (8.2.4)
\subsubsection[maxconn]{maxconn <conns>}
\index{maxconn}
Fix the maximum number of concurrent connections on a frontend
\dflb{yes}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<conns>] is the maximum number of concurrent connections the frontend will
accept to serve. Excess connections will be queued by the system
in the socket's listen queue and will be served once a connection
closes.
\end{description}
If the system supports it, it can be useful on big sites to raise this limit
very high so that haproxy manages connection queues, instead of leaving the
clients with unanswered connection attempts. This value should not exceed the
global maxconn. Also, keep in mind that a connection contains two buffers
of 8kB each, as well as some other data resulting in about 17 kB of RAM being
consumed per established connection. That means that a medium system equipped
with 1GB of RAM can withstand around 40000-50000 concurrent connections if
properly tuned.
Also, when <conns> is set to large values, it is possible that the servers
are not sized to accept such loads, and for this reason it is generally wise
to assign them some reasonable connection limits.
See also: "server", global section's "maxconn", "fullconn"
\subsubsection[mode]{mode \{ tcp | http | health \}}
\index{mode}
Set the running mode or protocol of the instance
\dflb{yes}{yes}{yes}{yes}
Arguments :
\begin{description}
\item[tcp] The instance will work in pure TCP mode. A full-duplex connection
will be established between clients and servers, and no layer 7
examination will be performed. This is the default mode. It
should be used for SSL, SSH, SMTP, ...
\item[http] The instance will work in HTTP mode. The client request will be
analyzed in depth before connecting to any server. Any request
which is not RFC-compliant will be rejected. Layer 7 filtering,
processing and switching will be possible. This is the mode which
brings HAProxy most of its value.
\item[health] The instance will work in "health" mode. It will just reply "OK"
to incoming connections and close the connection. Nothing will be
logged. This mode is used to reply to external components health
checks. This mode is deprecated and should not be used anymore as
it is possible to do the same and even better by combining TCP or
HTTP modes with the "monitor" keyword.
\end{description}
When doing content switching, it is mandatory that the frontend and the
backend are in the same mode (generally HTTP), otherwise the configuration
will be refused.
Example:
\begin{verbatim}
defaults http_instances
mode http
\end{verbatim}
See also: "monitor", "monitor-net"
\subsubsection[monitor fail]{monitor fail \{ if | unless \} <condition>}
\index{monitor fail}
Add a condition to report a failure to a monitor HTTP request.
\dflb{no}{yes}{yes}{no}
Arguments:
\begin{description}
\item[if <cond>] the monitor request will fail if the condition is satisfied,
and will succeed otherwise. The condition should describe a
combined test which must induce a failure if all conditions
are met, for instance a low number of servers both in a
backend and its backup.
\item[unless <cond>] the monitor request will succeed only if the condition is
satisfied, and will fail otherwise. Such a condition may be
based on a test on the presence of a minimum number of active
servers in a list of backends.
\end{description}
This statement adds a condition which can force the response to a monitor
request to report a failure. By default, when an external component queries
the URI dedicated to monitoring, a 200 response is returned. When one of the
conditions above is met, haproxy will return 503 instead of 200. This is
very useful to report a site failure to an external component which may base
routing advertisements between multiple sites on the availability reported by
haproxy. In this case, one would rely on an ACL involving the "nbsrv"
criterion. Note that "monitor fail" only works in HTTP mode. Both status
messages may be tweaked using "errorfile" or "errorloc" if needed.
Example:
\begin{verbatim}
frontend www
mode http
acl site_dead nbsrv(dynamic) lt 2
acl site_dead nbsrv(static) lt 2
monitor-uri /site_alive
monitor fail if site_dead
\end{verbatim}
See also: "monitor-net", "monitor-uri", "errorfile", "errorloc"
\subsubsection[monitor-net]{monitor-net <source>}
\index{monitor-net}
Declare a source network which is limited to monitor requests
\dflb{yes}{yes}{yes}{no}
Arguments:
\begin{description}
\item[ <source>] is the source IPv4 address or network which will only be able to
get monitor responses to any request. It can be either an IPv4
address, a host name, or an address followed by a slash ('\verb|/|')
followed by a mask.
\end{description}
In TCP mode, any connection coming from a source matching <source> will cause
the connection to be immediately closed without any log. This allows another
equipment to probe the port and verify that it is still listening, without
forwarding the connection to a remote server.
In HTTP mode, a connection coming from a source matching <source> will be
accepted, the following response will be sent without waiting for a request,
then the connection will be closed : "HTTP/1.0 200 OK". This is normally
enough for any front-end HTTP probe to detect that the service is UP and
running without forwarding the request to a backend server.
Monitor requests are processed very early. It is not possible to block nor
divert them using ACLs. They cannot be logged either, and it is the intended
purpose. They are only used to report HAProxy's health to an upper component,
nothing more. Right now, it is not possible to set failure conditions on
requests caught by "monitor-net".
Last, please note that only one "monitor-net" statement can be specified in
a frontend. If more than one is found, only the last one will be considered.
Example:
\begin{verbatim}
# addresses .252 and .253 are just probing us.
frontend www
monitor-net 192.168.0.252/31
\end{verbatim}
See also : "monitor fail", "monitor-uri"
\subsubsection[monitor-uri]{monitor-uri <uri>}
\index{monitor-uri}
Intercept a URI used by external components' monitor requests
\dflb{yes}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<uri>] is the exact URI which we want to intercept to return HAProxy's
health status instead of forwarding the request.
\end{description}
When an HTTP request referencing <uri> will be received on a frontend,
HAProxy will not forward it nor log it, but instead will return either
"HTTP/1.0 200 OK" or "HTTP/1.0 503 Service unavailable", depending on failure
conditions defined with "monitor fail". This is normally enough for any
front-end HTTP probe to detect that the service is UP and running without
forwarding the request to a backend server. Note that the HTTP method, the
version and all headers are ignored, but the request must at least be valid
at the HTTP level. This keyword may only be used with an HTTP-mode frontend.
Monitor requests are processed very early. It is not possible to block nor
divert them using ACLs. They cannot be logged either, and it is the intended
purpose. They are only used to report HAProxy's health to an upper component,
nothing more. However, it is possible to add any number of conditions using
"monitor fail" and ACLs so that the result can be adjusted to whatever check
can be imagined (most often the number of available servers in a backend).
Example :
\begin{verbatim}
# Use /haproxy_test to report haproxy's status
frontend www
mode http
monitor-uri /haproxy_test
\end{verbatim}
See also: "monitor fail", "monitor-net"
\subsubsection{option abortonclose}
\subsubsection{no option abortonclose}
\index{abortonclose}
Enable or disable early dropping of aborted requests pending in queues.
\dflb{yes}{no}{yes}{yes}
Arguments: none
In presence of very high loads, the servers will take some time to respond.
The per-instance connection queue will inflate, and the response time will
increase respective to the size of the queue times the average per-session
response time. When clients will wait for more than a few seconds, they will
often hit the "STOP" button on their browser, leaving a useless request in
the queue, and slowing down other users, and the servers as well, because the
request will eventually be served, then aborted at the first error
encountered while delivering the response.
As there is no way to distinguish between a full STOP and a simple output
close on the client side, HTTP agents should be conservative and consider
that the client might only have closed its output channel while waiting for
the response. However, this introduces risks of congestion when lots of users
do the same, and is completely useless nowadays because probably no client at
all will close the session while waiting for the response. Some HTTP agents
support this behaviour (Squid, Apache, HAProxy), and others do not (TUX, most
hardware-based load balancers). So the probability for a closed input channel
to represent a user hitting the "STOP" button is close to 100%, and the risk
of being the single component to break rare but valid traffic is extremely
low, which adds to the temptation to be able to abort a session early while
still not served and not pollute the servers.
In HAProxy, the user can choose the desired behaviour using the option
"abortonclose". By default (without the option) the behaviour is HTTP
compliant and aborted requests will be served. But when the option is
specified, a session with an incoming channel closed will be aborted while
it is still possible, either pending in the queue for a connection slot, or
during the connection establishment if the server has not yet acknowledged
the connection request. This considerably reduces the queue size and the load
on saturated servers when users are tempted to click on STOP, which in turn
reduces the response time for other users.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "timeout queue" and server's "maxconn" and "maxqueue" parameters
\subsubsection{option accept-invalid-http-request}
\subsubsection{no option accept-invalid-http-request}
\index{accept-invalid-http-request}
Enable or disable relaxing of HTTP request parsing
\dflb{yes}{yes}{yes}{no}
Arguments: none
By default, HAProxy complies with RFC2616 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option. Similarly, the
list of characters allowed to appear in a URI is well defined by RFC3986, and
chars 0-31, 32 (space), 34 ('\verb|"|'), 60 ('\verb|<|'), 62 ('\verb|>|'), 92 ('\verb|\|'), 94 ('\verb|^|'), 96
('\verb|`|'), 123 ('\verb|{|'), 124 ('\verb:|:'), 125 ('\verb|}|'), 127 (delete) and anything above are
not allowed at all. Haproxy always blocks a number of them (0..32, 127). The
remaining ones are blocked by default unless this option is enabled.
This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.
When this option is enabled, erroneous header names will still be accepted in
requests, but the complete request will be captured in order to permit later
analysis using the "show errors" request on the UNIX stats socket. Similarly,
requests containing invalid chars in the URI part will be logged. Doing this
also helps confirming that the issue has been solved.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option accept-invalid-http-response" and "show errors" on the
stats socket.
\subsubsection{option accept-invalid-http-response}
\subsubsection{no option accept-invalid-http-response}
\index{accept-invalid-http-response}
Enable or disable relaxing of HTTP response parsing
\dflb{yes}{no}{yes}{yes}
Arguments: none
By default, HAProxy complies with RFC2616 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option.
This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.
When this option is enabled, erroneous header names will still be accepted in
responses, but the complete response will be captured in order to permit
later analysis using the "show errors" request on the UNIX stats socket.
Doing this also helps confirming that the issue has been solved.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option accept-invalid-http-request" and "show errors" on the
stats socket.
\subsubsection{option allbackups}
\subsubsection{no option allbackups}
\index{allbackups}
Use either all backup servers at a time or only the first one
\dflb{yes}{no}{yes}{yes}
Arguments: none
By default, the first operational backup server gets all traffic when normal
servers are all down. Sometimes, it may be preferred to use multiple backups
at once, because one will not be enough. When "option allbackups" is enabled,
the load balancing will be performed among all backup servers when all normal
ones are unavailable. The same load balancing algorithm will be used and the
servers' weights will be respected. Thus, there will not be any priority
order between the backup servers anymore.
This option is mostly used with static server farms dedicated to return a
"sorry" page when an application is completely offline.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
\subsubsection{option checkcache}
\subsubsection{no option checkcache}
\index{checkcache}
Analyze all server responses and block requests with cacheable cookies
\dflb{yes}{no}{yes}{yes}
Arguments : none
Some high-level frameworks set application cookies everywhere and do not
always let enough control to the developer to manage how the responses should
be cached. When a session cookie is returned on a cacheable object, there is a
high risk of session crossing or stealing between users traversing the same
caches. In some situations, it is better to block the response than to let
some sensitive session information go in the wild.
The option "checkcache" enables deep inspection of all server responses for
strict compliance with HTTP specification in terms of cacheability. It
carefully checks "Cache-control", "Pragma" and "Set-cookie" headers in server
response to check if there's a risk of caching a cookie on a client-side
proxy. When this option is enabled, the only responses which can be delivered
to the client are:
\begin{itemize}
\item[-] all those without "Set-Cookie" header ;
\item[-] all those with a return code other than 200, 203, 206, 300, 301, 410,
provided that the server has not set a "Cache-control: public" header ;
\item[-] all those that come from a POST request, provided that the server has not
set a 'Cache-Control: public' header ;
\item[-] those with a 'Pragma: no-cache' header
\item[-] those with a 'Cache-control: private' header
\item[-] those with a 'Cache-control: no-store' header
\item[-] those with a 'Cache-control: max-age=0' header
\item[-] those with a 'Cache-control: s-maxage=0' header
\item[-] those with a 'Cache-control: no-cache' header
\item[-] those with a 'Cache-control: no-cache="set-cookie"' header
\item[-] those with a 'Cache-control: no-cache="set-cookie,' header
(allowing other fields after set-cookie)
\end{itemize}
If a response doesn't respect these requirements, then it will be blocked
just as if it was from an "rspdeny" filter, with an "HTTP 502 bad gateway".
The session state shows "PH--" meaning that the proxy blocked the response
during headers processing. Additionally, an alert will be sent in the logs so
that admins are informed that there's something to be fixed.
Due to the high impact on the application, the application should be tested
in depth with the option enabled before going to production. It is also a
good practice to always activate it during tests, even if it is not used in
production, as it will report potentially dangerous application behaviors.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
\subsubsection{option clitcpka}
\subsubsection{no option clitcpka}
\index{clitcpka}
Enable or disable the sending of TCP keepalive packets on the client side
\dflb{yes}{yes}{yes}{no}
Arguments: none
When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (eg: remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.
Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.
It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.
Please note that this has nothing to do with HTTP keep-alive.
Using option "clitcpka" enables the emission of TCP keep-alive probes on the
client side of a connection, which should help when session expirations are
noticed between HAProxy and a client.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option srvtcpka", "option tcpka"
\subsubsection{option contstats}
\index{contstats}
Enable continuous traffic statistics updates
\dflb{yes}{yes}{yes}{no}
Arguments: none
By default, counters used for statistics calculation are incremented
only when a session finishes. It works quite well when serving small
objects, but with big ones (for example large images or archives) or
with A/V streaming, a graph generated from haproxy counters looks like
a hedgehog. With this option enabled counters get incremented continuously,
during a whole session. Recounting touches a hotpath directly so
it is not enabled by default, as it has small performance impact (\~{}0.5\%).
\subsubsection{option dontlog-normal}
\subsubsection{no option dontlog-normal}
\index{dontlog-normal}
Enable or disable logging of normal, successful connections
\dflb{yes}{yes}{yes}{no}
Arguments: none
There are large sites dealing with several thousand connections per second
and for which logging is a major pain. Some of them are even forced to turn
logs off and cannot debug production issues. Setting this option ensures that
normal connections, those which experience no error, no timeout, no retry nor
redispatch, will not be logged. This leaves disk space for anomalies. In HTTP
mode, the response status code is checked and return codes 5xx will still be
logged.
It is strongly discouraged to use this option as most of the time, the key to
complex issues is in the normal logs which will not be logged here. If you
need to separate logs, see the "log-separate-errors" option instead.
See also: "log", "dontlognull", "log-separate-errors" and section 8 about
logging.
\subsubsection{option dontlognull}
\subsubsection{no option dontlognull}
\index{dontlognull}
Enable or disable logging of null connections
\dflb{yes}{yes}{yes}{no}
Arguments: none
In certain environments, there are components which will regularly connect to
various systems to ensure that they are still alive. It can be the case from
another load balancer as well as from monitoring systems. By default, even a
simple port probe or scan will produce a log. If those connections pollute
the logs too much, it is possible to enable option "dontlognull" to indicate
that a connection on which no data has been transferred will not be logged,
which typically corresponds to those probes.
It is generally recommended not to use this option in uncontrolled
environments (eg: internet), otherwise scans and other malicious activities
would not be logged.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "log", "monitor-net", "monitor-uri" and section 8 about logging.
\subsubsection{option forceclose}
\subsubsection{no option forceclose}
\index{forceclose}
Enable or disable active connection closing after response is transferred.
\dflb{yes}{yes}{yes}{yes}
Arguments: none
Some HTTP servers do not necessarily close the connections when they receive
the "Connection: close" set by "option httpclose", and if the client does not
close either, then the connection remains open till the timeout expires. This
causes high number of simultaneous connections on the servers and shows high
global session times in the logs.
When this happens, it is possible to use "option forceclose". It will
actively close the outgoing server channel as soon as the server has finished
to respond. This option implicitly enables the "httpclose" option. Note that
this option also enables the parsing of the full request and response, which
means we can close the connection to the server very quickly, releasing some
resources earlier than with httpclose.
This option may also be combined with "option http-pretend-keepalive", which
will disable sending of the "Connection: close" header, but will still cause
the connection to be closed once the whole response is received.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option httpclose" and "option http-pretend-keepalive"
\subsubsection[option forwardfor]{option forwardfor [ except <network> ] [ header <name> ] [ if-none ]}
\index{forwardfor}
Enable insertion of the X-Forwarded-For header to requests sent to servers
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<network>] is an optional argument used to disable this option for sources
matching <network>
\item[<name>] an optional argument to specify a different "X-Forwarded-For"
header name.
\end{description}
Since HAProxy works in reverse-proxy mode, the servers see its IP address as
their client address. This is sometimes annoying when the client's IP address
is expected in server logs. To solve this problem, the well-known HTTP header
"X-Forwarded-For" may be added by HAProxy to all requests sent to the server.
This header contains a value representing the client's IP address. Since this
header is always appended at the end of the existing header list, the server
must be configured to always use the last occurrence of this header only. See
the server's manual to find how to enable use of this standard header. Note
that only the last occurrence of the header must be used, since it is really
possible that the client has already brought one.
The keyword "header" may be used to supply a different header name to replace
the default "X-Forwarded-For". This can be useful where you might already
have a "X-Forwarded-For" header from a different application (eg: stunnel),
and you need preserve it. Also if your backend server doesn't use the
"X-Forwarded-For" header and requires different one (eg: Zeus Web Servers
require "X-Cluster-Client-IP").
Sometimes, a same HAProxy instance may be shared between a direct client
access and a reverse-proxy access (for instance when an SSL reverse-proxy is
used to decrypt HTTPS traffic). It is possible to disable the addition of the
header for a known source address or network by adding the "except" keyword
followed by the network address. In this case, any source IP matching the
network will not cause an addition of this header. Most common uses are with
private networks or 127.0.0.1.
Alternatively, the keyword "if-none" states that the header will only be
added if it is not present. This should only be used in perfectly trusted
environment, as this might cause a security issue if headers reaching haproxy
are under the control of the end-user.
This option may be specified either in the frontend or in the backend. If at
least one of them uses it, the header will be added. Note that the backend's
setting of the header subargument takes precedence over the frontend's if
both are defined. In the case of the "if-none" argument, if at least one of
the frontend or the backend does not specify it, it wants the addition to be
mandatory, so it wins.
It is important to note that by default, HAProxy works in tunnel mode and
only inspects the first request of a connection, meaning that only the first
request will have the header appended, which is certainly not what you want.
In order to fix this, ensure that any of the "httpclose", "forceclose" or
"http-server-close" options is set when using this option.
Examples:
\begin{verbatim}
# Public HTTP address also used by stunnel on the same machine
frontend www
mode http
option forwardfor except 127.0.0.1 # stunnel already adds the header
# Those servers want the IP Address in X-Client
backend www
mode http
option forwardfor header X-Client
\end{verbatim}
See also: "option httpclose", "option http-server-close",
"option forceclose"
\subsubsection{option http-no-delay}
\subsubsection{no option http-no-delay}
\index{http-no-delay}
Instruct the system to favor low interactive delays over performance in HTTP
\dflb{yes}{yes}{yes}{yes}
Arguments: none
In HTTP, each payload is unidirectional and has no notion of interactivity.
Any agent is expected to queue data somewhat for a reasonably low delay.
There are some very rare server-to-server applications that abuse the HTTP
protocol and expect the payload phase to be highly interactive, with many
interleaved data chunks in both directions within a single request. This is
absolutely not supported by the HTTP specification and will not work across
most proxies or servers. When such applications attempt to do this through
haproxy, it works but they will experience high delays due to the network
optimizations which favor performance by instructing the system to wait for
enough data to be available in order to only send full packets. Typical
delays are around 200 ms per round trip. Note that this only happens with
abnormal uses. Normal uses such as CONNECT requests nor WebSockets are not
affected.
When "option http-no-delay" is present in either the frontend or the backend
used by a connection, all such optimizations will be disabled in order to
make the exchanges as fast as possible. Of course this offers no guarantee on
the functionality, as it may break at any other place. But if it works via
HAProxy, it will work as fast as possible. This option should never be used
by default, and should never be used at all unless such a buggy application
is discovered. The impact of using this option is an increase of bandwidth
usage and CPU usage, which may significantly lower performance in high
latency environments.
\subsubsection{option http-pretend-keepalive}
\subsubsection{no option http-pretend-keepalive}
\index{http-pretend-keepalive}
Define whether haproxy will announce keepalive to the server or not
\dflb{yes}{yes}{yes}{yes}
Arguments: none
When running with "option http-server-close" or "option forceclose", haproxy
adds a "Connection: close" header to the request forwarded to the server.
Unfortunately, when some servers see this header, they automatically refrain
from using the chunked encoding for responses of unknown length, while this
is totally unrelated. The immediate effect is that this prevents haproxy from
maintaining the client connection alive. A second effect is that a client or
a cache could receive an incomplete response without being aware of it, and
consider the response complete.
By setting "option http-pretend-keepalive", haproxy will make the server
believe it will keep the connection alive. The server will then not fall back
to the abnormal undesired above. When haproxy gets the whole response, it
will close the connection with the server just as it would do with the
"forceclose" option. That way the client gets a normal response and the
connection is correctly closed on the server side.
It is recommended not to enable this option by default, because most servers
will more efficiently close the connection themselves after the last packet,
and release its buffers slightly earlier. Also, the added packet on the
network could slightly reduce the overall peak performance. However it is
worth noting that when this option is enabled, haproxy will have slightly
less work to do. So if haproxy is the bottleneck on the whole architecture,
enabling this option might save a few CPU cycles.
This option may be set both in a frontend and in a backend. It is enabled if
at least one of the frontend or backend holding a connection has it enabled.
This option may be combined with "option httpclose", which will cause
keepalive to be announced to the server and close to be announced to the
client. This practice is discouraged though.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also : "option forceclose" and "option http-server-close"
\subsubsection{option http-server-close}
\subsubsection{no option http-server-close}
\index{http-server-close}
Enable or disable HTTP connection closing on the server side
\dflb{yes}{yes}{yes}{yes}
Arguments: none
By default, when a client communicates with a server, HAProxy will only
analyze, log, and process the first request of each connection. Setting
"option http-server-close" enables HTTP connection-close mode on the server
side while keeping the ability to support HTTP keep-alive and pipelining on
the client side. This provides the lowest latency on the client side (slow
network) and the fastest session reuse on the server side to save server
resources, similarly to "option forceclose". It also permits non-keepalive
capable servers to be served in keep-alive mode to the clients if they
conform to the requirements of RFC2616. Please note that some servers do not
always conform to those requirements when they see "Connection: close" in the
request. The effect will be that keep-alive will never be used. A workaround
consists in enabling "option http-pretend-keepalive".
At the moment, logs will not indicate whether requests came from the same
session or not. The accept date reported in the logs corresponds to the end
of the previous request, and the request time corresponds to the time spent
waiting for a new request. The keep-alive request time is still bound to the
timeout defined by "timeout http-keep-alive" or "timeout http-request" if
not set.
This option may be set both in a frontend and in a backend. It is enabled if
at least one of the frontend or backend holding a connection has it enabled.
It is worth noting that "option forceclose" has precedence over "option
http-server-close" and that combining "http-server-close" with "httpclose"
basically achieve the same result as "forceclose".
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option forceclose", "option http-pretend-keepalive",
"option httpclose" and "1.1. The HTTP transaction model".
\subsubsection{option http-use-proxy-header}
\subsubsection{no option http-use-proxy-header}
\index{http-use-proxy-header}
Make use of non-standard Proxy-Connection header instead of Connection
\dflb{yes}{yes}{yes}{no}
Arguments: none
While RFC2616 explicitly states that HTTP/1.1 agents must use the
Connection header to indicate their wish of persistent or non-persistent
connections, both browsers and proxies ignore this header for proxied
connections and make use of the undocumented, non-standard Proxy-Connection
header instead. The issue begins when trying to put a load balancer between
browsers and such proxies, because there will be a difference between what
haproxy understands and what the client and the proxy agree on.
By setting this option in a frontend, haproxy can automatically switch to use
that non-standard header if it sees proxied requests. A proxied request is
defined here as one where the URI begins with neither a '\verb|/|' nor a '\verb|*|'. The
choice of header only affects requests passing through proxies making use of
one of the "httpclose", "forceclose" and "http-server-close" options. Note
that this option can only be specified in a frontend and will affect the
request along its whole life.
Also, when this option is set, a request which requires authentication will
automatically switch to use proxy authentication headers if it is itself a
proxied request. That makes it possible to check or enforce authentication in
front of an existing proxy.
This option should normally never be used, except in front of a proxy.
See also: "option httpclose", "option forceclose" and "option
http-server-close".
\subsubsection{option httpchk}
\subsubsection*{option httpchk <uri>}
\subsubsection*{option httpchk <method> <uri>}
\subsubsection*{option httpchk <method> <uri> <version>}
\index{httpchk}
Enable HTTP protocol to check on the servers health
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<method>] is the optional HTTP method used with the requests. When not set,
the "OPTIONS" method is used, as it generally requires low server
processing and is easy to filter out from the logs. Any method
may be used, though it is not recommended to invent non-standard
ones.
\item[<uri>] is the URI referenced in the HTTP requests. It defaults to "\verb|/|"
which is accessible by default on almost any server, but may be
changed to any other URI. Query strings are permitted.
\item[<version>] is the optional HTTP version string. It defaults to "HTTP/1.0"
but some servers might behave incorrectly in HTTP 1.0, so turning
it to HTTP/1.1 may sometimes help. Note that the Host field is
mandatory in HTTP/1.1, and as a trick, it is possible to pass it
after "\verb|\r\n|" following the version string.
\end{description}
By default, server health checks only consist in trying to establish a TCP
connection. When "option httpchk" is specified, a complete HTTP request is
sent once the TCP connection is established, and responses 2xx and 3xx are
considered valid, while all other ones indicate a server failure, including
the lack of any response.
The port and interval are specified in the server configuration.
This option does not necessarily require an HTTP backend, it also works with
plain TCP backends. This is particularly useful to check simple scripts bound
to some dedicated ports using the inetd daemon.
Examples :
\begin{verbatim}
# Relay HTTPS traffic to Apache instance and check service availability
# using HTTP request "OPTIONS * HTTP/1.1" on port 80.
backend https_relay
mode tcp
option httpchk OPTIONS * HTTP/1.1\r\nHost:\ www
server apache1 192.168.1.1:443 check port 80
\end{verbatim}
See also: "option ssl-hello-chk", "option smtpchk", "option mysql-check",
"option pgsql-check", "http-check" and the "check", "port" and
"inter" server options.
\subsubsection{option httpclose}
\subsubsection{no option httpclose}
\index{httpclose}
Enable or disable passive HTTP connection closing
\dflb{yes}{yes}{yes}{yes}
Arguments: none
By default, when a client communicates with a server, HAProxy will only
analyze, log, and process the first request of each connection. If "option
httpclose" is set, it will check if a "Connection: close" header is already
set in each direction, and will add one if missing. Each end should react to
this by actively closing the TCP connection after each transfer, thus
resulting in a switch to the HTTP close mode. Any "Connection" header
different from "close" will also be removed.
It seldom happens that some servers incorrectly ignore this header and do not
close the connection eventhough they reply "Connection: close". For this
reason, they are not compatible with older HTTP 1.0 browsers. If this happens
it is possible to use the "option forceclose" which actively closes the
request connection once the server responds. Option "forceclose" also
releases the server connection earlier because it does not have to wait for
the client to acknowledge it.
This option may be set both in a frontend and in a backend. It is enabled if
at least one of the frontend or backend holding a connection has it enabled.
If "option forceclose" is specified too, it has precedence over "httpclose".
If "option http-server-close" is enabled at the same time as "httpclose", it
basically achieves the same result as "option forceclose".
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also : "option forceclose", "option http-server-close" and
"1.1. The HTTP transaction model".
\subsubsection[option httplog]{option httplog [ clf ]}
\index{httplog}
Enable logging of HTTP request, session state and timers
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[clf] if the "clf" argument is added, then the output format will be
the CLF format instead of HAProxy's default HTTP format. You can
use this when you need to feed HAProxy's logs through a specific
log analyser which only support the CLF format and which is not
extensible.
\end{description}
By default, the log output format is very poor, as it only contains the
source and destination addresses, and the instance name. By specifying
"option httplog", each log line turns into a much richer format including,
but not limited to, the HTTP request, the connection timers, the session
status, the connections numbers, the captured headers and cookies, the
frontend, backend and server name, and of course the source address and
ports.
This option may be set either in the frontend or the backend.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it. Specifying
only "option httplog" will automatically clear the 'clf' mode if it was set
by default.
See also: section 8 about logging.
\subsubsection{option http\_proxy}
\subsubsection{no option http\_proxy}
\index{http\_proxy}
Enable or disable plain HTTP proxy mode
\dflb{yes}{yes}{yes}{yes}
Arguments: none
It sometimes happens that people need a pure HTTP proxy which understands
basic proxy requests without caching nor any fancy feature. In this case,
it may be worth setting up an HAProxy instance with the "option http\_proxy"
set. In this mode, no server is declared, and the connection is forwarded to
the IP address and port found in the URL after the "\verb|http://|" scheme.
No host address resolution is performed, so this only works when pure IP
addresses are passed. Since this option's usage perimeter is rather limited,
it will probably be used only by experts who know they need exactly it. Last,
if the clients are susceptible of sending keep-alive requests, it will be
needed to add "option httpclose" to ensure that all requests will correctly
be analyzed.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
Example:
\begin{verbatim}
# this backend understands HTTP proxy requests and forwards them directly.
backend direct_forward
option httpclose
option http_proxy
\end{verbatim}
See also: "option httpclose"
\subsubsection{option independant-streams}
\subsubsection{no option independant-streams}
\index{independant-streams}
Enable or disable independant timeout processing for both directions
\dflb{yes}{yes}{yes}{yes}
Arguments: none
By default, when data is sent over a socket, both the write timeout and the
read timeout for that socket are refreshed, because we consider that there is
activity on that socket, and we have no other means of guessing if we should
receive data or not.
While this default behavior is desirable for almost all applications, there
exists a situation where it is desirable to disable it, and only refresh the
read timeout if there are incoming data. This happens on sessions with large
timeouts and low amounts of exchanged data such as telnet session. If the
server suddenly disappears, the output data accumulates in the system's
socket buffers, both timeouts are correctly refreshed, and there is no way
to know the server does not receive them, so we don't timeout. However, when
the underlying protocol always echoes sent data, it would be enough by itself
to detect the issue using the read timeout. Note that this problem does not
happen with more verbose protocols because data won't accumulate long in the
socket buffers.
When this option is set on the frontend, it will disable read timeout updates
on data sent to the client. There probably is little use of this case. When
the option is set on the backend, it will disable read timeout updates on
data sent to the server. Doing so will typically break large HTTP posts from
slow lines, so use it with caution.
See also: "timeout client", "timeout server" and "timeout tunnel"
\subsubsection{option ldap-check}
\index{ldap-check}
Use LDAPv3 health checks for server testing
\dflb{yes}{no}{yes}{yes}
Arguments: none
It is possible to test that the server correctly talks LDAPv3 instead of just
testing that it accepts the TCP connection. When this option is set, an
LDAPv3 anonymous simple bind message is sent to the server, and the response
is analyzed to find an LDAPv3 bind response message.
The server is considered valid only when the LDAP response contains success resultCode.
\verb|http://tools.ietf.org/html/rfc4511#section-4.1.9|
Logging of bind requests is server dependent see your documentation how to
configure it.
Example:
\begin{verbatim}
option ldap-check
\end{verbatim}
See also: "option httpchk"
\subsubsection{option log-health-checks}
\subsubsection{no option log-health-checks}
\index{log-health-checks}
Enable or disable logging of health checks
\dflb{yes}{no}{yes}{yes}
Arguments : none
Enable health checks logging so it possible to check for example what
was happening before a server crash. Failed health check are logged if
server is UP and succeeded health checks if server is DOWN, so the amount
of additional information is limited.
If health check logging is enabled no health check status is printed
when servers is set up UP/DOWN/ENABLED/DISABLED.
See also: "log" and section 8 about logging.
\subsubsection{option log-separate-errors}
\subsubsection{no option log-separate-errors}
\index{log-separate-errors}
Change log level for non-completely successful connections
\dflb{yes}{yes}{yes}{no}
Arguments: none
Sometimes looking for errors in logs is not easy. This option makes haproxy
raise the level of logs containing potentially interesting information such
as errors, timeouts, retries, redispatches, or HTTP status codes 5xx. The
level changes from "info" to "err". This makes it possible to log them
separately to a different file with most syslog daemons. Be careful not to
remove them from the original file, otherwise you would lose ordering which
provides very important information.
Using this option, large sites dealing with several thousand connections per
second may log normal traffic to a rotating buffer and only archive smaller
error logs.
See also: "log", "dontlognull", "dontlog-normal" and section 8 about
logging.
\subsubsection{option logasap}
\subsubsection{no option logasap}
\index{logasap}
Enable or disable early logging of HTTP requests
\dflb{yes}{yes}{yes}{no}
Arguments: none
By default, HTTP requests are logged upon termination so that the total
transfer time and the number of bytes appear in the logs. When large objects
are being transferred, it may take a while before the request appears in the
logs. Using "option logasap", the request gets logged as soon as the server
sends the complete headers. The only missing information in the logs will be
the total number of bytes which will indicate everything except the amount
of data transferred, and the total time which will not take the transfer
time into account. In such a situation, it's a good practice to capture the
"Content-Length" response header so that the logs at least indicate how many
bytes are expected to be transferred.
Examples:
\begin{verbatim}
listen http_proxy 0.0.0.0:80
mode http
option httplog
option logasap
log 192.168.2.200 local3
>>> Feb 6 12:14:14 localhost \
haproxy[14389]: 10.0.1.2:33317 [06/Feb/2009:12:14:14.655] http-in \
static/srv1 9/10/7/14/+30 200 +243 - - ---- 3/1/1/1/0 1/0 \
"GET /image.iso HTTP/1.0"
\end{verbatim}
See also : "option httplog", "capture response header", and section 8 about
logging.
\subsubsection[option mysql-check]{option mysql-check [ user <username> ]}
\index{mysql-check}
Use MySQL health checks for server testing
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<username>] This is the username which will be used when connecting to MySQL
server.
\end{description}
If you specify a username, the check consists of sending two MySQL packet,
one Client Authentication packet, and one QUIT packet, to correctly close
MySQL session. We then parse the MySQL Handshake Initialisation packet and/or
Error packet. It is a basic but useful test which does not produce error nor
aborted connect on the server. However, it requires adding an authorization
in the MySQL table, like this:
\begin{verbatim}
USE mysql;
INSERT INTO user (Host,User) values ('<ip_of_haproxy>','<username>');
FLUSH PRIVILEGES;
\end{verbatim}
If you don't specify a username (it is deprecated and not recommended), the
check only consists in parsing the Mysql Handshake Initialization packet or
Error packet, we don't send anything in this mode. It was reported that it
can generate lockout if check is too frequent and/or if there is not enough
traffic. In fact, you need in this case to check MySQL "max\_connect\_errors"
value as if a connection is established successfully within fewer than MySQL
"max\_connect\_errors" attempts after a previous connection was interrupted,
the error count for the host is cleared to zero. If HAProxy's server get
blocked, the "FLUSH HOSTS" statement is the only way to unblock it.
Remember that this does not check database presence nor database consistency.
To do this, you can use an external check with xinetd for example.
The check requires MySQL >=3.22, for older version, please use TCP check.
Most often, an incoming MySQL server needs to see the client's IP address for
various purposes, including IP privilege matching and connection logging.
When possible, it is often wise to masquerade the client's IP address when
connecting to the server using the "usesrc" argument of the "source" keyword,
which requires the cttproxy feature to be compiled in, and the MySQL server
to route the client via the machine hosting haproxy.
See also: "option httpchk"
\subsubsection[option pgsql-check]{option pgsql-check [ user <username> ]}
\index{pgsql-check}
Use PostgreSQL health checks for server testing
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<username>] This is the username which will be used when connecting to
PostgreSQL server.
\end{description}
The check sends a PostgreSQL StartupMessage and waits for either
Authentication request or ErrorResponse message. It is a basic but useful
test which does not produce error nor aborted connect on the server.
This check is identical with the "mysql-check".
See also: "option httpchk"
\subsubsection{option nolinger}
\subsubsection{no option nolinger}
\index{nolinger}
Enable or disable immediate session resource cleaning after close
\dflb{yes}{yes}{yes}{yes}
Arguments: none
When clients or servers abort connections in a dirty way (eg: they are
physically disconnected), the session timeouts triggers and the session is
closed. But it will remain in FIN\_WAIT1 state for some time in the system,
using some resources and possibly limiting the ability to establish newer
connections.
When this happens, it is possible to activate "option nolinger" which forces
the system to immediately remove any socket's pending data on close. Thus,
the session is instantly purged from the system's tables. This usually has
side effects such as increased number of TCP resets due to old retransmits
getting immediately rejected. Some firewalls may sometimes complain about
this too.
For this reason, it is not recommended to use this option when not absolutely
needed. You know that you need it when you have thousands of FIN\_WAIT1
sessions on your system (TIME\_WAIT ones do not count).
This option may be used both on frontends and backends, depending on the side
where it is required. Use it on the frontend for clients, and on the backend
for servers.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
\subsubsection[option originalto]{option originalto [ except <network> ] [ header <name> ]}
\index{originalto}
Enable insertion of the X-Original-To header to requests sent to servers
\dflb{yes}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<network>] is an optional argument used to disable this option for sources
matching <network>
\item[<name>] an optional argument to specify a different "X-Original-To"
header name.
\end{description}
Since HAProxy can work in transparent mode, every request from a client can
be redirected to the proxy and HAProxy itself can proxy every request to a
complex SQUID environment and the destination host from SO\_ORIGINAL\_DST will
be lost. This is annoying when you want access rules based on destination ip
addresses. To solve this problem, a new HTTP header "X-Original-To" may be
added by HAProxy to all requests sent to the server. This header contains a
value representing the original destination IP address. Since this must be
configured to always use the last occurrence of this header only. Note that
only the last occurrence of the header must be used, since it is really
possible that the client has already brought one.
The keyword "header" may be used to supply a different header name to replace
the default "X-Original-To". This can be useful where you might already
have a "X-Original-To" header from a different application, and you need
preserve it. Also if your backend server doesn't use the "X-Original-To"
header and requires different one.
Sometimes, a same HAProxy instance may be shared between a direct client
access and a reverse-proxy access (for instance when an SSL reverse-proxy is
used to decrypt HTTPS traffic). It is possible to disable the addition of the
header for a known source address or network by adding the "except" keyword
followed by the network address. In this case, any source IP matching the
network will not cause an addition of this header. Most common uses are with
private networks or 127.0.0.1.
This option may be specified either in the frontend or in the backend. If at
least one of them uses it, the header will be added. Note that the backend's
setting of the header subargument takes precedence over the frontend's if
both are defined.
It is important to note that by default, HAProxy works in tunnel mode and
only inspects the first request of a connection, meaning that only the first
request will have the header appended, which is certainly not what you want.
In order to fix this, ensure that any of the "httpclose", "forceclose" or
"http-server-close" options is set when using this option.
Examples :
\begin{verbatim}
# Original Destination address
frontend www
mode http
option originalto except 127.0.0.1
# Those servers want the IP Address in X-Client-Dst
backend www
mode http
option originalto header X-Client-Dst
\end{verbatim}
See also: "option httpclose", "option http-server-close",
"option forceclose"
\subsubsection{option persist}
\subsubsection{no option persist}
\index{persist}
Enable or disable forced persistence on down servers
\dflb{yes}{no}{yes}{yes}
Arguments: none
When an HTTP request reaches a backend with a cookie which references a dead
server, by default it is redispatched to another server. It is possible to
force the request to be sent to the dead server first using "option persist"
if absolutely needed. A common use case is when servers are under extreme
load and spend their time flapping. In this case, the users would still be
directed to the server they opened the session on, in the hope they would be
correctly served. It is recommended to use "option redispatch" in conjunction
with this option so that in the event it would not be possible to connect to
the server at all (server definitely dead), the client would finally be
redirected to another valid server.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option redispatch", "retries", "force-persist"
\subsubsection{option redispatch}
\subsubsection{no option redispatch}
\index{redispatch}
Enable or disable session redistribution in case of connection failure
\dflb{yes}{no}{yes}{yes}
Arguments: none
In HTTP mode, if a server designated by a cookie is down, clients may
definitely stick to it because they cannot flush the cookie, so they will not
be able to access the service anymore.
Specifying "option redispatch" will allow the proxy to break their
persistence and redistribute them to a working server.
It also allows to retry last connection to another server in case of multiple
connection failures. Of course, it requires having "retries" set to a nonzero
value.
This form is the preferred form, which replaces both the "redispatch" and
"redisp" keywords.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "redispatch", "retries", "force-persist"
\subsubsection{option redis-check}
\index{redis-check}
Use redis health checks for server testing
\dflb{yes}{no}{yes}{yes}
Arguments: none
It is possible to test that the server correctly talks REDIS protocol instead
of just testing that it accepts the TCP connection. When this option is set,
a PING redis command is sent to the server, and the response is analyzed to
find the "+PONG" response message.
Example:
\begin{verbatim}
option redis-check
\end{verbatim}
See also: "option httpchk"
\subsubsection{option smtpchk}
\subsubsection*{option smtpchk <hello> <domain>}
\index{smtpchk}
Use SMTP health checks for server testing
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<hello>] is an optional argument. It is the "hello" command to use. It can
be either "HELO" (for SMTP) or "EHLO" (for ESTMP). All other
values will be turned into the default command ("HELO").
\item[<domain>] is the domain name to present to the server. It may only be
specified (and is mandatory) if the hello command has been
specified. By default, "localhost" is used.
\end{description}
When "option smtpchk" is set, the health checks will consist in TCP
connections followed by an SMTP command. By default, this command is
"HELO localhost". The server's return code is analyzed and only return codes
starting with a "2" will be considered as valid. All other responses,
including a lack of response will constitute an error and will indicate a
dead server.
This test is meant to be used with SMTP servers or relays. Depending on the
request, it is possible that some servers do not log each connection attempt,
so you may want to experiment to improve the behavior. Using telnet on port
25 is often easier than adjusting the configuration.
Most often, an incoming SMTP server needs to see the client's IP address for
various purposes, including spam filtering, anti-spoofing and logging. When
possible, it is often wise to masquerade the client's IP address when
connecting to the server using the "usesrc" argument of the "source" keyword,
which requires the cttproxy feature to be compiled in.
Example:
\begin{verbatim}
option smtpchk HELO mydomain.org
\end{verbatim}
See also: "option httpchk", "source"
\subsubsection{option socket-stats}
\subsubsection{no option socket-stats}
\index{socket-stats}
Enable or disable collecting \& providing separate statistics for each socket.
\dflb{yes}{yes}{yes}{no}
Arguments: none
\subsubsection{option splice-auto}
\subsubsection{no option splice-auto}
\index{splice-auto}
Enable or disable automatic kernel acceleration on sockets in both directions
\dflb{yes}{yes}{yes}{yes}
Arguments: none
When this option is enabled either on a frontend or on a backend, haproxy
will automatically evaluate the opportunity to use kernel tcp splicing to
forward data between the client and the server, in either direction. Haproxy
uses heuristics to estimate if kernel splicing might improve performance or
not. Both directions are handled independently. Note that the heuristics used
are not much aggressive in order to limit excessive use of splicing. This
option requires splicing to be enabled at compile time, and may be globally
disabled with the global option "nosplice". Since splice uses pipes, using it
requires that there are enough spare pipes.
Important note: kernel-based TCP splicing is a Linux-specific feature which
first appeared in kernel 2.6.25. It offers kernel-based acceleration to
transfer data between sockets without copying these data to user-space, thus
providing noticeable performance gains and CPU cycles savings. Since many
early implementations are buggy, corrupt data and/or are inefficient, this
feature is not enabled by default, and it should be used with extreme care.
While it is not possible to detect the correctness of an implementation,
2.6.29 is the first version offering a properly working implementation. In
case of doubt, splicing may be globally disabled using the global "nosplice"
keyword.
Example:
\begin{verbatim}
option splice-auto
\end{verbatim}
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option splice-request", "option splice-response", and global
options "nosplice" and "maxpipes"
\subsubsection{option splice-request}
\subsubsection{no option splice-request}
\index{splice-request}
Enable or disable automatic kernel acceleration on sockets for requests
\dflb{yes}{yes}{yes}{yes}
Arguments: none
When this option is enabled either on a frontend or on a backend, haproxy
will user kernel tcp splicing whenever possible to forward data going from
the client to the server. It might still use the recv/send scheme if there
are no spare pipes left. This option requires splicing to be enabled at
compile time, and may be globally disabled with the global option "nosplice".
Since splice uses pipes, using it requires that there are enough spare pipes.
\emph{Important note:} see "option splice-auto" for usage limitations.
Example:
\begin{verbatim}
option splice-request
\end{verbatim}
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option splice-auto", "option splice-response", and global options
"nosplice" and "maxpipes"
\subsubsection{option splice-response}
\subsubsection{no option splice-response}
\index{splice-response}
Enable or disable automatic kernel acceleration on sockets for responses
\dflb{yes}{yes}{yes}{yes}
Arguments: none
When this option is enabled either on a frontend or on a backend, haproxy
will user kernel tcp splicing whenever possible to forward data going from
the server to the client. It might still use the recv/send scheme if there
are no spare pipes left. This option requires splicing to be enabled at
compile time, and may be globally disabled with the global option "nosplice".
Since splice uses pipes, using it requires that there are enough spare pipes.
\emph{Important note:} see "option splice-auto" for usage limitations.
Example:
\begin{verbatim}
option splice-response
\end{verbatim}
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option splice-auto", "option splice-request", and global options
"nosplice" and "maxpipes"
\subsubsection{option srvtcpka}
\subsubsection{no option srvtcpka}
\index{srvtcpka}
Enable or disable the sending of TCP keepalive packets on the server side
\dflb{yes}{no}{yes}{yes}
Arguments : none
When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (eg: remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.
Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.
It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.
Please note that this has nothing to do with HTTP keep-alive.
Using option "srvtcpka" enables the emission of TCP keep-alive probes on the
server side of a connection, which should help when session expirations are
noticed between HAProxy and a server.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option clitcpka", "option tcpka"
\subsubsection{option ssl-hello-chk}
\index{ssl-hello-chk}
Use SSLv3 client hello health checks for server testing
\dflb{yes}{no}{yes}{yes}
Arguments: none
When some SSL-based protocols are relayed in TCP mode through HAProxy, it is
possible to test that the server correctly talks SSL instead of just testing
that it accepts the TCP connection. When "option ssl-hello-chk" is set, pure
SSLv3 client hello messages are sent once the connection is established to
the server, and the response is analyzed to find an SSL server hello message.
The server is considered valid only when the response contains this server
hello message.
All servers tested till there correctly reply to SSLv3 client hello messages,
and most servers tested do not even log the requests containing only hello
messages, which is appreciable.
See also: "option httpchk"
\subsubsection{option tcp-smart-accept}
\subsubsection{no option tcp-smart-accept}
\index{tcp-smart-accept}
Enable or disable the saving of one ACK packet during the accept sequence
\dflb{yes}{yes}{yes}{no}
Arguments : none
When an HTTP connection request comes in, the system acknowledges it on
behalf of HAProxy, then the client immediately sends its request, and the
system acknowledges it too while it is notifying HAProxy about the new
connection. HAProxy then reads the request and responds. This means that we
have one TCP ACK sent by the system for nothing, because the request could
very well be acknowledged by HAProxy when it sends its response.
For this reason, in HTTP mode, HAProxy automatically asks the system to avoid
sending this useless ACK on platforms which support it (currently at least
Linux). It must not cause any problem, because the system will send it anyway
after 40 ms if the response takes more time than expected to come.
During complex network debugging sessions, it may be desirable to disable
this optimization because delayed ACKs can make troubleshooting more complex
when trying to identify where packets are delayed. It is then possible to
fall back to normal behavior by specifying "no option tcp-smart-accept".
It is also possible to force it for non-HTTP proxies by simply specifying
"option tcp-smart-accept". For instance, it can make sense with some services
such as SMTP where the server speaks first.
It is recommended to avoid forcing this option in a defaults section. In case
of doubt, consider setting it back to automatic values by prepending the
"default" keyword before it, or disabling it using the "no" keyword.
See also: "option tcp-smart-connect"
\subsubsection{option tcp-smart-connect}
\subsubsection{no option tcp-smart-connect}
\index{tcp-smart-connect}
Enable or disable the saving of one ACK packet during the connect sequence
\dflb{yes}{no}{yes}{yes}
Arguments: none
On certain systems (at least Linux), HAProxy can ask the kernel not to
immediately send an empty ACK upon a connection request, but to directly
send the buffer request instead. This saves one packet on the network and
thus boosts performance. It can also be useful for some servers, because they
immediately get the request along with the incoming connection.
This feature is enabled when "option tcp-smart-connect" is set in a backend.
It is not enabled by default because it makes network troubleshooting more
complex.
It only makes sense to enable it with protocols where the client speaks first
such as HTTP. In other situations, if there is no data to send in place of
the ACK, a normal ACK is sent.
If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.
See also: "option tcp-smart-accept"
\subsubsection{option tcpka}
\index{tcpka}
Enable or disable the sending of TCP keepalive packets on both sides
\dflb{yes}{yes}{yes}{yes}
Arguments: none
When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (eg: remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.
Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.
It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.
Please note that this has nothing to do with HTTP keep-alive.
Using option "tcpka" enables the emission of TCP keep-alive probes on both
the client and server sides of a connection. Note that this is meaningful
only in "defaults" or "listen" sections. If this option is used in a
frontend, only the client side will get keep-alives, and if this option is
used in a backend, only the server side will get keep-alives. For this
reason, it is strongly recommended to explicitly use "option clitcpka" and
"option srvtcpka" when the configuration is split between frontends and
backends.
See also: "option clitcpka", "option srvtcpka"
\subsubsection{option tcplog}
\index{tcplog}
Enable advanced logging of TCP connections with session state and timers
\dflb{yes}{yes}{yes}{yes}
Arguments: none
By default, the log output format is very poor, as it only contains the
source and destination addresses, and the instance name. By specifying
"option tcplog", each log line turns into a much richer format including, but
not limited to, the connection timers, the session status, the connections
numbers, the frontend, backend and server name, and of course the source
address and ports. This option is useful for pure TCP proxies in order to
find which of the client or server disconnects or times out. For normal HTTP
proxies, it's better to use "option httplog" which is even more complete.
This option may be set either in the frontend or the backend.
See also: "option httplog", and section 8 about logging.
\subsubsection{option transparent}
\subsubsection{no option transparent}
\index{transparent}
Enable client-side transparent proxying
\dflb{yes}{no}{yes}{yes}
Arguments: none
This option was introduced in order to provide layer 7 persistence to layer 3
load balancers. The idea is to use the OS's ability to redirect an incoming
connection for a remote address to a local process (here HAProxy), and let
this process know what address was initially requested. When this option is
used, sessions without cookies will be forwarded to the original destination
IP address of the incoming request (which should match that of another
equipment), while requests with cookies will still be forwarded to the
appropriate server.
Note that contrary to a common belief, this option does NOT make HAProxy
present the client's IP to the server when establishing the connection.
See also: the "usesrc" argument of the "source" keyword, and the
"transparent" option of the "bind" keyword.
\subsubsection{persist rdp-cookie}
\subsubsection*{persist rdp-cookie(<name>)}
\index{persist rdp-cookie}
Enable RDP cookie-based persistence
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<name>] is the optional name of the RDP cookie to check. If omitted, the
default cookie name "msts" will be used. There currently is no
valid reason to change this name.
\end{description}
This statement enables persistence based on an RDP cookie. The RDP cookie
contains all information required to find the server in the list of known
servers. So when this option is set in the backend, the request is analysed
and if an RDP cookie is found, it is decoded. If it matches a known server
which is still UP (or if "option persist" is set), then the connection is
forwarded to this server.
Note that this only makes sense in a TCP backend, but for this to work, the
frontend must have waited long enough to ensure that an RDP cookie is present
in the request buffer. This is the same requirement as with the "rdp-cookie"
load-balancing method. Thus it is highly recommended to put all statements in
a single "listen" section.
Also, it is important to understand that the terminal server will emit this
RDP cookie only if it is configured for "token redirection mode", which means
that the "IP address redirection" option is disabled.
Example:
\begin{verbatim}
listen tse-farm
bind :3389
# wait up to 5s for an RDP cookie in the request
tcp-request inspect-delay 5s
tcp-request content accept if RDP_COOKIE
# apply RDP cookie persistence
persist rdp-cookie
# if server is unknown, let's balance on the same cookie.
# alternatively, "balance leastconn" may be useful too.
balance rdp-cookie
server srv1 1.1.1.1:3389
server srv2 1.1.1.2:3389
\end{verbatim}
See also: "balance rdp-cookie", "tcp-request", the "req\_rdp\_cookie" ACL and
the rdp\_cookie pattern fetch function.
\subsubsection[rate-limit sessions]{rate-limit sessions <rate>}
\index{rate-limit sessions}
Set a limit on the number of new sessions accepted per second on a frontend.
\dflb{yes}{yes}{yes}{no}
Arguments:
\begin{description}
\item[<rate>] The <rate> parameter is an integer designating the maximum number
of new sessions per second to accept on the frontend.
\end{description}
When the frontend reaches the specified number of new sessions per second, it
stops accepting new connections until the rate drops below the limit again.
During this time, the pending sessions will be kept in the socket's backlog
(in system buffers) and haproxy will not even be aware that sessions are
pending. When applying very low limit on a highly loaded service, it may make
sense to increase the socket's backlog using the "backlog" keyword.
This feature is particularly efficient at blocking connection-based attacks
or service abuse on fragile servers. Since the session rate is measured every
millisecond, it is extremely accurate. Also, the limit applies immediately,
no delay is needed at all to detect the threshold.
Example: limit the connection rate on SMTP to 10 per second max
\begin{verbatim}
listen smtp
mode tcp
bind :25
rate-limit sessions 10
server 127.0.0.1:1025
\end{verbatim}
\emph{Note:} when the maximum rate is reached, the frontend's status is not changed
but its sockets appear as "WAITING" in the statistics if the
"socket-stats" option is enabled.
See also: the "backlog" keyword and the "fe\_sess\_rate" ACL criterion.
\subsubsection[redirect location] {redirect location <to> [code <code>] <option> [{if | unless} <condition>]}
\subsubsection[redirect prefix] {redirect prefix <to> [code <code>] <option> [{if | unless} <condition>]}
\index{redirect location}
\index{redirect prefix}
Return an HTTP redirection if/unless a condition is matched
\dflb{no}{yes}{yes}{yes}
If/unless the condition is matched, the HTTP request will lead to a redirect
response. If no condition is specified, the redirect applies unconditionally.
Arguments:
\begin{description}
\item[<to>] With "redirect location", the exact value in <to> is placed into
the HTTP "Location" header. In case of "redirect prefix", the
"Location" header is built from the concatenation of <to> and the
complete URI, including the query string, unless the "drop-query"
option is specified (see below). As a special case, if <to>
equals exactly "\verb|/|" in prefix mode, then nothing is inserted
before the original URI. It allows one to redirect to the same
URL.
\item[<code>] The code is optional. It indicates which type of HTTP redirection
is desired. Only codes 301, 302 and 303 are supported, and 302 is
used if no code is specified. 301 means "Moved permanently", and
a browser may cache the Location. 302 means "Moved permanently"
and means that the browser should not cache the redirection. 303
is equivalent to 302 except that the browser will fetch the
location with a GET method.
\item[<option>] There are several options which can be specified to adjust the
expected behavior of a redirection:
\begin{itemize}
\item[-] "drop-query"
When this keyword is used in a prefix-based redirection, then the
location will be set without any possible query-string, which is useful
for directing users to a non-secure page for instance. It has no effect
with a location-type redirect.
\item[-] "append-slash"
This keyword may be used in conjunction with "drop-query" to redirect
users who use a URL not ending with a '\verb|/|' to the same one with the '\verb|/|'.
It can be useful to ensure that search engines will only see one URL.
For this, a return code 301 is preferred.
\item[-] "set-cookie NAME[=value]"
A "Set-Cookie" header will be added with NAME (and optionally "=value")
to the response. This is sometimes used to indicate that a user has
been seen, for instance to protect against some types of DoS. No other
cookie option is added, so the cookie will be a session cookie. Note
that for a browser, a sole cookie name without an equal sign is
different from a cookie with an equal sign.
\item[-] "clear-cookie NAME[=]"
A "Set-Cookie" header will be added with NAME (and optionally "\verb|=|"), but
with the "Max-Age" attribute set to zero. This will tell the browser to
delete this cookie. It is useful for instance on logout pages. It is
important to note that clearing the cookie "NAME" will not remove a
cookie set with "NAME=value". You have to clear the cookie "NAME=" for
that, because the browser makes the difference.
\end{itemize}
\end{description}
Example: move the login URL only to HTTPS.
\begin{verbatim}
acl clear dst_port 80
acl secure dst_port 8080
acl login_page url_beg /login
acl logout url_beg /logout
acl uid_given url_reg /login?userid=[^&]+
acl cookie_set hdr_sub(cookie) SEEN=1
redirect prefix https://mysite.com set-cookie SEEN=1 if !cookie_set
redirect prefix https://mysite.com if login_page !secure
redirect prefix http://mysite.com drop-query if login_page !uid_given
redirect location http://mysite.com/ if !login_page secure
redirect location / clear-cookie USERID= if logout
\end{verbatim}
Example: send redirects for request for articles without a '\verb|/|'.
\begin{verbatim}
acl missing_slash path_reg ^/article/[^/]*$
redirect code 301 prefix / drop-query append-slash if missing_slash
\end{verbatim}
See section 7 about ACL usage.
\subsubsection[redisp]{redisp (deprecated)}
\subsubsection[redispatch]{redispatch (deprecated)}
\index{redisp}
\index{redispatch}
Enable or disable session redistribution in case of connection failure
\dflb{yes}{no}{yes}{yes}
Arguments: none
In HTTP mode, if a server designated by a cookie is down, clients may
definitely stick to it because they cannot flush the cookie, so they will not
be able to access the service anymore.
Specifying "redispatch" will allow the proxy to break their persistence and
redistribute them to a working server.
It also allows to retry last connection to another server in case of multiple
connection failures. Of course, it requires having "retries" set to a nonzero
value.
This form is deprecated, do not use it in any new configuration, use the new
"option redispatch" instead.
See also: "option redispatch"
\subsubsection[reqadd]{reqadd <string> [ \{if | unless\} <cond> ]}
\index{reqadd}
Add a header at the end of the HTTP request
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<string>] is the complete line to be added. Any space or known delimiter
must be escaped using a backslash ('\verb|\|'). Please refer to section
6 about HTTP header manipulation for more information.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
A new line consisting in <string> followed by a line feed will be added after
the last header of an HTTP request.
Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses.
Example : add "X-Proto: SSL" to requests coming via port 81
\begin{verbatim}
acl is-ssl dst_port 81
reqadd X-Proto:\ SSL if is-ssl
\end{verbatim}
See also: "rspadd", section 6 about HTTP header manipulation, and section 7
about ACLs.
\subsubsection[reqallow]{reqallow <search> [ \{if | unless\} <cond> ]}
\subsubsection[reqiallow]{reqiallow <search> [ \{if | unless\} <cond> ] (ignore case)}
\index{reqallow}
\index{reqiallow}
Definitely allow an HTTP request if a line matches a regular expression
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
request line. This is an extended regular expression. Parenthesis
grouping is supported and no preliminary backslash is required.
Any space or known delimiter must be escaped using a backslash
('\verb|\|'). The pattern applies to a full line at a time. The
"reqallow" keyword strictly matches case while "reqiallow"
ignores case.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
A request containing any line which matches extended regular expression
<search> will mark the request as allowed, even if any later test would
result in a deny. The test applies both to the request line and to request
headers. Keep in mind that URLs in request line are case-sensitive while
header names are not.
It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.
Example: allow www.* but refuse *.local
\begin{verbatim}
reqiallow ^Host:\ www\.
reqideny ^Host:\ .*\.local
\end{verbatim}
See also: "reqdeny", "block", section 6 about HTTP header manipulation, and
section 7 about ACLs.
\subsubsection[reqdel]{reqdel <search> [ \{if | unless\} <cond>]}
\subsubsection[reqidel]{reqidel <search> [ \{if | unless\} <cond>] (ignore case)}
\index{reqdel}
\index{reqidel}
Delete all headers matching a regular expression in an HTTP request
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
request line. This is an extended regular expression. Parenthesis
grouping is supported and no preliminary backslash is required.
Any space or known delimiter must be escaped using a backslash
('\verb|\|'). The pattern applies to a full line at a time. The "reqdel"
keyword strictly matches case while "reqidel" ignores case.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
Any header line matching extended regular expression <search> in the request
will be completely deleted. Most common use of this is to remove unwanted
and/or dangerous headers or cookies from a request before passing it to the
next servers.
Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Keep in mind that header names are not case-sensitive.
Example: remove X-Forwarded-For header and SERVER cookie
\begin{verbatim}
reqidel ^X-Forwarded-For:.*
reqidel ^Cookie:.*SERVER=
\end{verbatim}
See also: "reqadd", "reqrep", "rspdel", section 6 about HTTP header
manipulation, and section 7 about ACLs.
\subsubsection[reqdeny]{reqdeny <search> [ \{if | unless\} <cond> ]}
\subsubsection[reqideny]{reqideny <search> [ \{if | unless\} <cond> ] (ignore case)}
\index{reqdeny}
\index{reqideny}
Deny an HTTP request if a line matches a regular expression
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
request line. This is an extended regular expression. Parenthesis
grouping is supported and no preliminary backslash is required.
Any space or known delimiter must be escaped using a backslash
('\verb|\|'). The pattern applies to a full line at a time. The
"reqdeny" keyword strictly matches case while "reqideny" ignores
case.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
A request containing any line which matches extended regular expression
<search> will mark the request as denied, even if any later test would
result in an allow. The test applies both to the request line and to request
headers. Keep in mind that URLs in request line are case-sensitive while
header names are not.
A denied request will generate an "HTTP 403 forbidden" response once the
complete request has been parsed. This is consistent with what is practiced
using ACLs.
It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.
Example: refuse *.local, then allow www.*
\begin{verbatim}
reqideny ^Host:\ .*\.local
reqiallow ^Host:\ www\.
\end{verbatim}
See also: "reqallow", "rspdeny", "block", section 6 about HTTP header
manipulation, and section 7 about ACLs.
\subsubsection[reqpass]{reqpass <search> [ \{if | unless\} <cond>] }
\subsubsection[reqipass]{reqipass <search> [ \{if | unless\} <cond>] (ignore case) }
\index{reqpass}
\index{reqipass}
Ignore any HTTP request line matching a regular expression in next rules
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
request line. This is an extended regular expression. Parenthesis
grouping is supported and no preliminary backslash is required.
Any space or known delimiter must be escaped using a backslash
('\verb|\|'). The pattern applies to a full line at a time. The
"reqpass" keyword strictly matches case while "reqipass" ignores
case.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
A request containing any line which matches extended regular expression
<search> will skip next rules, without assigning any deny or allow verdict.
The test applies both to the request line and to request headers. Keep in
mind that URLs in request line are case-sensitive while header names are not.
It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.
Example: refuse *.local, then allow www.*, but ignore "www.private.local"
\begin{verbatim}
reqipass ^Host:\ www.private\.local
reqideny ^Host:\ .*\.local
reqiallow ^Host:\ www\.
\end{verbatim}
See also: "reqallow", "reqdeny", "block", section 6 about HTTP header
manipulation, and section 7 about ACLs.
\subsubsection[reqrep]{reqrep <search> <string> [ \{if | unless\} <cond> ]}
\subsubsection[reqirep]{reqirep <search> <string> [ \{if | unless\} <cond> ] (ignore case)}
\index{reqrep}
\index{reqirep}
Replace a regular expression with a string in an HTTP request line
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
request line. This is an extended regular expression. Parenthesis
grouping is supported and no preliminary backslash is required.
Any space or known delimiter must be escaped using a backslash
('\verb|\|'). The pattern applies to a full line at a time. The "reqrep"
keyword strictly matches case while "reqirep" ignores case.
\item[<string>] is the complete line to be added. Any space or known delimiter
must be escaped using a backslash ('\verb|\|'). References to matched
pattern groups are possible using the common \verb|\N| form, with N
being a single digit between 0 and 9. Please refer to section
6 about HTTP header manipulation for more information.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
Any line matching extended regular expression <search> in the request (both
the request line and header lines) will be completely replaced with <string>.
Most common use of this is to rewrite URLs or domain names in "Host" headers.
Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Note that for increased readability, it is suggested to add enough
spaces between the request and the response. Keep in mind that URLs in
request line are case-sensitive while header names are not.
Example: replace "/static/" with "/" at the beginning of any request path.
\begin{verbatim}
reqrep ^([^\ :]*)\ /static/(.*) \1\ /\2
# replace "www.mydomain.com" with "www" in the host name.
reqirep ^Host:\ www.mydomain.com Host:\ www
\end{verbatim}
See also: "reqadd", "reqdel", "rsprep", section 6 about HTTP header
manipulation, and section 7 about ACLs.
\subsubsection[reqtarpit]{reqtarpit <search> [ \{if | unless\} <cond> ]}
\subsubsection[reqitarpit]{reqitarpit <search> [ \{if | unless\} <cond> ] (ignore case)}
\index{reqtarpit}
\index{reqitarpit}
Tarpit an HTTP request containing a line matching a regular expression
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
request line. This is an extended regular expression. Parenthesis
grouping is supported and no preliminary backslash is required.
Any space or known delimiter must be escaped using a backslash
('\verb|\|'). The pattern applies to a full line at a time. The
"reqtarpit" keyword strictly matches case while "reqitarpit"
ignores case.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
A request containing any line which matches extended regular expression
<search> will be tarpitted, which means that it will connect to nowhere, will
be kept open for a pre-defined time, then will return an HTTP error 500 so
that the attacker does not suspect it has been tarpitted. The status 500 will
be reported in the logs, but the completion flags will indicate "PT". The
delay is defined by "timeout tarpit", or "timeout connect" if the former is
not set.
The goal of the tarpit is to slow down robots attacking servers with
identifiable requests. Many robots limit their outgoing number of connections
and stay connected waiting for a reply which can take several minutes to
come. Depending on the environment and attack, it may be particularly
efficient at reducing the load on the network and firewalls.
Examples: ignore user-agents reporting any flavour of "Mozilla" or "MSIE", but block all others.
\begin{verbatim}
reqipass ^User-Agent:\.*(Mozilla|MSIE)
reqitarpit ^User-Agent:
# block bad guys
acl badguys src 10.1.0.3 172.16.13.20/28
reqitarpit . if badguys
\end{verbatim}
See also: "reqallow", "reqdeny", "reqpass", section 6 about HTTP header
manipulation, and section 7 about ACLs.
\subsubsection[retries]{retries <value>}
\index{retries}
Set the number of retries to perform on a server after a connection failure
\dflb{yes}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<value>] is the number of times a connection attempt should be retried on
a server when a connection either is refused or times out. The
default value is 3.
\end{description}
It is important to understand that this value applies to the number of
connection attempts, not full requests. When a connection has effectively
been established to a server, there will be no more retry.
In order to avoid immediate reconnections to a server which is restarting,
a turn-around timer of 1 second is applied before a retry occurs.
When "option redispatch" is set, the last retry may be performed on another
server even if a cookie references a different server.
See also: "option redispatch"
\subsubsection[rspadd]{rspadd <string> [ \{if | unless\} <cond>] }
\index{rspadd}
Add a header at the end of the HTTP response
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<string>] is the complete line to be added. Any space or known delimiter
must be escaped using a backslash ('\verb|\|'). Please refer to section
6 about HTTP header manipulation for more information.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
A new line consisting in <string> followed by a line feed will be added after
the last header of an HTTP response.
Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses.
See also: "reqadd", section 6 about HTTP header manipulation, and section 7
about ACLs.
\subsubsection[rspdel]{rspdel <search> [ \{if | unless\} <cond> ]}
\subsubsection[rspidel]{<search> [ \{if | unless\} <cond> ] (ignore case)}
\index{rspdel}
\index{rspidel}
Delete all headers matching a regular expression in an HTTP response
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
response line. This is an extended regular expression, so
parenthesis grouping is supported and no preliminary backslash
is required. Any space or known delimiter must be escaped using
a backslash ('\verb|\|'). The pattern applies to a full line at a time.
The "rspdel" keyword strictly matches case while "rspidel"
ignores case.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
Any header line matching extended regular expression <search> in the response
will be completely deleted. Most common use of this is to remove unwanted
and/or sensitive headers or cookies from a response before passing it to the
client.
Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Keep in mind that header names are not case-sensitive.
Example: remove the Server header from responses
\begin{verbatim}
reqidel ^Server:.*
\end{verbatim}
See also: "rspadd", "rsprep", "reqdel", section 6 about HTTP header
manipulation, and section 7 about ACLs.
\subsubsection[rspdeny] {rspdeny <search> [ \{if | unless\} <cond> ]}
\subsubsection[rspideny] {rspideny <search> [ \{if | unless\} <cond> ] (ignore case)}
\index{rspdeny}
\index{rspideny}
Block an HTTP response if a line matches a regular expression
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
response line. This is an extended regular expression, so
parenthesis grouping is supported and no preliminary backslash
is required. Any space or known delimiter must be escaped using
a backslash ('\verb|\|'). The pattern applies to a full line at a time.
The "rspdeny" keyword strictly matches case while "rspideny"
ignores case.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
A response containing any line which matches extended regular expression
<search> will mark the request as denied. The test applies both to the
response line and to response headers. Keep in mind that header names are not
case-sensitive.
Main use of this keyword is to prevent sensitive information leak and to
block the response before it reaches the client. If a response is denied, it
will be replaced with an HTTP 502 error so that the client never retrieves
any sensitive data.
It is easier, faster and more powerful to use ACLs to write access policies.
Rspdeny should be avoided in new designs.
Example: ensure that no content type matching ms-word will leak
\begin{verbatim}
rspideny ^Content-type:\.*/ms-word
\end{verbatim}
See also: "reqdeny", "acl", "block", section 6 about HTTP header manipulation
and section 7 about ACLs.
\subsubsection[rsprep]{rsprep <search> <string> [ \{if | unless\} <cond> ]}
\subsubsection[rspirep]{rspirep <search> <string> [ \{if | unless\} <cond> ] (ignore case)}
\index{rsprep}
\index{rspirep}
Replace a regular expression with a string in an HTTP response line
\dflb{no}{yes}{yes}{yes}
Arguments:
\begin{description}
\item[<search>] is the regular expression applied to HTTP headers and to the
response line. This is an extended regular expression, so
parenthesis grouping is supported and no preliminary backslash
is required. Any space or known delimiter must be escaped using
a backslash ('\verb|\|'). The pattern applies to a full line at a time.
The "rsprep" keyword strictly matches case while "rspirep"
ignores case.
\item[<string>] is the complete line to be added. Any space or known delimiter
must be escaped using a backslash ('\verb|\|'). References to matched
pattern groups are possible using the common \verb|\N| form, with N
being a single digit between 0 and 9. Please refer to section
6 about HTTP header manipulation for more information.
\item[<cond>] is an optional matching condition built from ACLs. It makes it
possible to ignore this rule when other conditions are not met.
\end{description}
Any line matching extended regular expression <search> in the response (both
the response line and header lines) will be completely replaced with
<string>. Most common use of this is to rewrite Location headers.
Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Note that for increased readability, it is suggested to add enough
spaces between the request and the response. Keep in mind that header names
are not case-sensitive.
Example: replace "Location: 127.0.0.1:8080" with "Location: www.mydomain.com"
\begin{verbatim}
rspirep ^Location:\ 127.0.0.1:8080 Location:\ www.mydomain.com
\end{verbatim}
See also: "rspadd", "rspdel", "reqrep", section 6 about HTTP header
manipulation, and section 7 about ACLs.
\subsubsection[server]{server <name> <address>[:[port]] [param*]}
\index{server}
Declare a server in a backend
\dflb{no}{no}{yes}{yes}
Arguments:
\begin{description}
\item[<name>] is the internal name assigned to this server. This name will
appear in logs and alerts. If "http-send-server-name" is
set, it will be added to the request header sent to the server.
\item[<address>] is the IPv4 or IPv6 address of the server. Alternatively, a
resolvable hostname is supported, but this name will be resolved
during start-up. Address "0.0.0.0" or "*" has a special meaning.
It indicates that the connection will be forwarded to the same IP
address as the one from the client connection. This is useful in
transparent proxy architectures where the client's connection is
intercepted and haproxy must forward to the original destination
address. This is more or less what the "transparent" keyword does
except that with a server it's possible to limit concurrency and
to report statistics.