A nginx module to add a sticky cookie to be always forwarded the the same upstream server.
When dealing with several backend servers, it's sometimes useful that one client (browser) is always served by the same backend server (for session persistance for example).
Using a persistance by IP (with the ip_hash upstream module) is maybe not a good idea because there could be situations where a lot of different browsers are coming with the same IP address (behind proxies)and the load balancing system won't be fair.
Using a cookie to track the upstream server makes each browser unique.
When the sticky module can't apply, it switchs back to the classic Round Robin Upstream or returns a "Bad Gateway" (depending on the no_fallback flag).
Sticky module can't apply when cookies are not supported by the browser
Sticky module is based on a "best effort" algorithm. Its aim is not to handle security somehow. It's been made to ensure that normal users are always redirected to the same backend server: that's all!
You'll need to re-compile Nginx from source to include this module. Modify your compile of Nginx by adding the following directive (modified to suit your path of course):
./configure ... --add-module=/absolute/path/to/nginx-sticky-module
make
make install
upstream {
sticky;
server 127.0.0.1:9000;
server 127.0.0.1:9001;
server 127.0.0.1:9002;
}
sticky [name=route] [domain=.foo.bar] [path=/] [expires=1h] [hash=index|md5|sha1] [hmac hmac_key=private_key] [no_fallback];
- name: the name of the cookies used to track the persistant upstream srv
default: route
- domain: the domain in which the cookie will be valid
default: nothing. Let the browser handle this.
- path: the path in which the cookie will be valid
default: nothing. Let the browser handle this.
- expires: the validity duration of the cookie
default: nothing. It's a session cookie.
restriction: must be a duration greater than one second
- hash: the hash mechanism to encode upstream server. It cant' be used
with hmac.
md5|sha1: well known hash
index: it's not hashed, an in-memory index is used instead
it's quicker and the overhead is shorter
Warning: the matching against upstream servers list
is inconsistent. So, at reload, if upstreams servers
has changed, index values are not guaranted to
correspond to the same server as before!
USE IT WITH CAUTION and only if you need to!
default: md5
- hmac: the HMAC hash mechanism to encode upstream server
It's like the hash mechanism but it uses hmac_key
to secure the hashing. It can't be used with hash.
md5|sha1: well known hash
default: none. see hash.
-hmac_key: the key to use with hmac. It's mandatory when hmac is set
default: nothing.
-no_fallback: when this flag is set, nginx will return a 502 (Bad Gateway or
Proxy Error) if a request comes with a cookie and the
corresponding backend is unavailable.
see docs/sticky.{vsd,pdf}
http://code.google.com/p/nginx-sticky-module/
- Stress
- Code review
Jerome Loyet <jerome at loyet dot net>
This module is licenced under the BSD license.
Copyright (C) 2010 Jerome Loyet (jerome at loyet dot net)
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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