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== link:index.html[Index] -> link:other.html[Other information]
Other: Cherokee goodies
There are several important features of Cherokee that really do make a
difference in real-world production environments.
Cherokee bundles a one of a kind GUI to set up every available feature
without the need of editing any configuration files by hand. It is a
modern and easy to manage web application that allows to set up the
server with speed and ease. The interface is thoroughly documented
throughout Cherokee's documentation. Several security measures prevent
non authorized personnel from accessing the application, and one-time
passwords are generated each time the program is launched. This can be
used to give temporary access to a remote administrator.
The Swiss-army knife of the Cherokee bundle. This little tool enables
you, among other things, to rotate the logs with absolutely no
downtime at all. No connections are lost. No delay happens. It can
also be used to trace Cherokee's state on the fly, even remotely and
on production servers.
This tool has its own documentation under the
link:other_bundle_cherokee-tweak.html[cherokee-tweak] section.
X-Sendfile is a special, non-standard HTTP header that has been
supported by Cherokee for a while. At first you might think it is no
big deal, but think again.It can be enabled in any CGI, FastCGI, SCGI,
or uWSGI backend. Basically its job is to instruct the web server to
ignore the content of the response and replace it by whatever is
specified in the header. The main advantage of this is that it will be
Cherokee the one serving the file, making use of all its
optimizations. It is useful for processing script-output of e.g. php,
perl, ruby or any cgi.
This is particularly useful because it hands the load to Cherokee, all
the response headers from the backend are forwarded, the whole
application uses a lot less resources and performs several times
faster not having to worry about a task best suited for a web server.
You retain the ability to check for special privileges or dynamically
deciding anything contemplated by your backend's logic, you speed up
things a lot while having more resources freed, and you can even
specify the delivery of files outside of the web server's document
root path. Of course, this is to be done solely in controlled
environments. In short, it offers a huge performance gain at
absolutely no cost.
Note that the X-Sendfile feature also supports `X-Accel-Redirect`
header, a similar feature offered by other web servers.
This is to allow the migration of applications supporting it without
having to make major code rewrites.
Of course, this feature can be enabled or disabled in a per-rule
basis, so you can have several rules and handlers on your virtual
servers with the feature ON or OFF according to your needs.
Zero Downtime Updates, AKA "Graceful restart"
Cherokee has an ability hardly ever seen in any service delivering
application, be it web content, multimedia streaming or almost any
other server you can think of.
Whenever a configuration change is applied, it is immediately
reflected in the web server with no downtime requirements to restart
the server. Of course the connections that are already being served
will continue normally with the same parameters that where negotiated
with the requesting clients, but they will not be shut down just to
perform a menial task such as restarting the server.
It's a bit like changing the tires on your car while still driving.
In fact, this mechanism is not only limited to configuration
updates. Cherokee is so smart that it can even apply this to perform
full program upgrades. This means you can completely replace the
binaries for new ones, launch the enhanced versions and yet not suffer
any downtime. Zero connection losses, no lag associated. Guaranteed.
This might seem as just another cool feature, but is in fact
huge. Just think about it: an extremely high traffic site cannot
afford to be down. Ever. Not to upgrade the webserver. Not to enhance
it. Not to reflect a new configuration setting. Thousands of hits per
second depend on it.
With Cherokee you can cope with this and much more. With Cherokee, it's
easier done than said.
SSL Virtual Hosts
A problem arises when virtual hosts and SSL must be used
simultaneously. This is due to the fact that a web server cannot see
the hostname header when the SSL request is being processed. The first
thing that the server has to do is to connect with the other end by
using SSL/TLS. The user entered host part of the URI must match the
Common Name (CN) provided by the certificate. Since virtual hosts are
in use, the CN of the first available certificate may or may not match
the one specified in the early stages of TLS negotiation.
You might have been told elsewhere that named virtual hosts in SSL
cannot be supported without SNI (Server Name Indication) because a web
server cannot see the hostname header when the SSL request is being
processed. Technically this might have been correct in the past. The
first thing that the server has to do is to connect with the other end
by using SSL/TLS. The user entered host part of the URI must match the
Common Name (CN) provided by the certificate. Since virtual hosts are in
use, the CN of the first available certificate may or may not match
the one specified in the early stages of TLS negotiation.
However, nothing is forever.. and that applies to SSL/TLS connections
as well. Cherokee elegantly respins the SSL layer once it knows the
virtual server, and the magic occurs: SSL supporting several
certificates on the same IP address and port.
Cherokee supports the clean and standard method of dealing with this
issue called
link:[Server Name
Indication] (SNI) that sends the name of the virtual host during the
TLS negotiation.
If link:[SNI] is
supported by your SSL/TLS library, the SSL layer does not need to be
restarted. Since the host info can be put in the SSL handshake, things
will simply work as long as there is a web browser with SNI support at
the other side. Currently every modern web browser supports this, and
Cherokee has TLS SNI support for the OpenSSL backends.
Note that for SNI to work, client support is required. Web browsers
known to support it are Mozilla Firefox 2.0+ and Opera 8.0+ in all its
variants, Safari 3.2.1+ on OS X and Vista, Internet Explorer 7+
(Vista, not XP) or later, and Google Chrome (Vista, not XP).
When using SNI is not possible, other workarounds can still be
used. Check the link:cookbook_ssl.html[SSL recipe] of our
link:cookbook.html[cookbook] for more details.
Database load balancing
Ever heard of the *DB Access Layer*, AKA
In case you haven't, DBSlayer is a database abstraction and pooling
layer designed to be simple to use (it's a DB abstraction layer for
the web age built on top of HTTP and JSON).
Well, Cherokee ships our very own
link:modules_handlers_dbslayer.html[DBSlayer] handler that provides
the fastest implementation in existence. It also provides several
interesting enhancements.
The usage of this balancing mechanism is a blessing when you wish to
scale connection growth against the database layer without replicating
your databases to every web server. It is also useful when you have
problems like local connections overwhelming a local slave, local
slave database failures, or replication failures.
This feature delivers connection pooling, database abstraction to
enable easier migrations and administration, load balancing and
automatic fail over.
Reverse Proxy
Yes, that too! Cherokee also provides a state of the art
link:modules_handlers_proxy.html[HTTP reverse proxy] module. Check the
documentation for more details and give it a try.
And if that is not enough, you can always take a look at the rest of
the link:modules.html[modules] bundled with Cherokee.
Audio and video streaming
Both audio and video streaming are supported, intelligently handling
the available bandwidth to maximize service. Are you planning on being
the next Youtube? Take a look at the
link:modules_handlers_streaming.html[Streaming handler].
Secure downloads
A pretty nifty feature that has been having great acceptance is
Cherokee's capability of generating temporal URLs to serve hidden
file. The link:modules_handlers_secdownload.html[Hidden Downloads]
handler is exactly what you need if, for instance, you plan on serving
lots of files and want to be protected against automatic download
scripts. Of course that is not the sole use of this. Cherokee only
implements the security. From there on, the sky is the limit.
AND, OR and NOT rule types
These rule types have been fully implemented for a long time. The
things achievable by these rules are at the same time very powerful
and very complex. You can combine them with as much flexibility as you
Configuration Wizards
Another interesting feature is a project aimed at providing
configuration wizards as an easy way to deploy a set of standard
applications. The idea is to select an application from the list and
let the wizard configure Cherokee to be able to run such application
-say Wordpress, for instance-.
Even though the obtained configuration could not be perfect, it will
always be a good starting point to play with for further tuning.
Slowloris resilient
Slowloris is the name of a perl-based HTTP client that can be used to
perform DOS attacks on web servers. It uses a minimal amount of TCP
traffic to do so, and quite frankly the attack has been running amok
out in the wild with devastating effects for a lot of servers.
Guess what? Cherokee is resilient to Slowloris and is recommended as
an effective defense on many security guides, such as the
link:[Slowloris DOS
Mitigation Guide].
Statistics and usage graphs
Cherokee-Admin uses RRDtool to collect and display statistical
data. If this feature is enabled, you will access a wide variety of
information. Check the link:other_graphs.html[usage graphs] section
for more details.
Template subsystem
There is an advanced template subsystem used for both the
link:config_virtual_servers_evhost.html[Advanced Virtual Hosting]
module and the link:modules_loggers_custom.html[Custom logger].
These modules can perform macro substitution to provide fine-grained
control over their capabilities. The template subsystem provides
slicing support in pretty much the same way the Python syntax does, so
it can basically allow to use portion of the replacement strings
instead of the whole thing.
You can read more about the specifics of the syntax and practical
examples on the config_virtual_servers_evhost.html#slicing[Slicing]
section of the link:config_virtual_servers_evhost.html[Advanced
Virtual Hosting] documentation.
Front-line Cache
Cherokee has built-in support for efficient caching mechanisms. These
allow it to cache anything that passes by (whether static or dynamic
content), without having to depend on an additional caching layer such
as Squid or Varnish. Typically such layers inherently introduce
latency due to the round-trips associated to checking whether or not
the contents have already been cached. Since Cherokee can process all
of this on its own, this overhead can be totally avoided. Check out
the link:other_front_line_cache.html[Front-line Cache] documentation.