stud - The Scalable TLS Unwrapping Daemon
stud is a network proxy that terminates TLS/SSL connections and forwards the
unencrypted traffic to some backend. It's designed to handle 10s of thousands of
connections efficiently on multicore machines.
It follows a process-per-core model; a parent process spawns N children who
accept() on a common socket to distribute connected clients among them.
Within each child, asynchronous socket I/O is conducted across the local
OpenSSL's nonblocking API. By default,
stud has an overhead of ~200KB per connection--it preallocates
some buffer space for data in flight between frontend and backend.
stud has very few features--it's designed to be paired with an intelligent
backend like haproxy or nginx. It maintains a strict 1:1 connection pattern
with this backend handler so that the backend can dictate throttling behavior,
maxmium connection behavior, availability of service, etc.
stud will optionally write the client IP address as the first few octets
(depending on IPv4 or IPv6) to the backend--or provide that information
using HAProxy's PROXY protocol. In this way, backends who care about the
client IP can still access it even though
stud itself appears to be the
Thanks to a contribution from Emeric at Exceliance (the folks behind HAProxy),
a special build of
stud can be made that utilitizes shared memory to
use a common session cache between all child processes. This can speed up
stud deployments by avoiding client renegotiation.
Please be aware of the policy regarding releases, code stability, and security:
- In git, the tip of the master branch should always build on Linux and FreeBSD, and is likely to be as stable as any other changeset. A careful review of patches is conducted before being pushed to github.
- Periodically, a version tag will be pushed to github for an old(er)
changeset--0.1, 0.2, etc. These tags mark a particular release of
studthat has seen heavy testing and several weeks of production stability. Conservative users are advised to use a tag.
studhas optional builds that utilize shared memory-based SSL contexts to keep a session cache between many child processes. The use of these builds can dramatically speed up SSL handshakes on many-core deployments. However, it's important to acknowledge the inevitable theoretical security tradeoffs associated with the use of this (substantially more complex) binary. Therefore, the deeply paranoid are advised to use only the standard
studbinary at the cost of some performance.
Requirements and Limitations
libev >= 4 openssl (recent, >=1.0.0 recommended)
Stud currently works on Linux, OpenBSD, FreeBSD, and MacOSX. It has been tested the most heavily on Linux/x86_64.
While porting it to other POSIX platforms is likely trivial, it hasn't be done yet. Patches welcome!
If you're handling a large number of connections, you'll
probably want to raise
ulimit -n before running
It's very strongly recommended to not run
stud as root; ideally, it would
be run as a user ("stud", perhaps) that does nothing but run
will setuid (using -u) after binding if you need to bind to a low port (< 1024).
$ make $ sudo make install
The only required argument is a path to a PEM file that contains the certificate (or a chain of certificates) and private key.
Detail about the entire set of options can be found by invoking
Encryption Methods: --tls TLSv1 (default) --ssl SSLv3 (implies no TLSv1) -c CIPHER_SUITE set allowed ciphers (default is OpenSSL defaults) Socket: -b HOST,PORT backend [connect] (default is "127.0.0.1,8000") -f HOST,PORT frontend [bind] (default is "*,8443") Performance: -n CORES number of worker processes (default is 1) -B BACKLOG set listen backlog size (default is 100) -e ENGINE select OpenSSL hardware acceleration engine (default is 'any'); use 'none' to disable engines Security: -r PATH chroot -u USERNAME set gid/uid after binding the socket Logging: -q be quiet; emit only error messages -s send log message to syslog in addition to stderr/stdout Special: --write-ip write 1 octet with the IP family followed by the IP address in 4 (IPv4) or 16 (IPv6) octets little-endian to backend before the actual data --write-proxy write HaProxy's PROXY (IPv4 or IPv6) protocol line before actual data
stud uses no configuration file.
To use DH with stud, you will need to add some bytes to your pem file:
% openssl dhparam -rand - 1024 >> PEMFILE
Be sure to set your cipher suite appropriately: -c DHE-RSA-AES256-SHA
stud was originally written by Jamie Turner (@jamwt) and is maintained
by the Bump (http://bu.mp) server team. It currently (6/11) provides
server-side TLS termination for over 40 million Bump users.
* Colin Percival @cperciva -- early security audit and code review * Frank DENIS @jedisct1 -- port to BSD, IPv6 support, various fixes * Denis Bilenko -- HAProxy PROXY protocol support, chroot/setuid * Joe Damato -- Diffie-Hellman parameter loading * Benjamin Pineau -- Chained cert loading, various fixes, performance tweaks * Carl Perry/Dreamhost -- IPv6 PROXY support * Emeric Brun/Exceliance -- Session resumption and shared-memory session cache * Vladimir Dronnikov -- Logging cleanup * James Golick/BitLove Inc. -- SIGPIPE fixes and child-reaping * Joe Williams -- Syslog support * Jason Cook -- SSL option tweaks (performance) * Artur Bergman -- Socket tweaks (performance)