[nginx] new upstream module // sticky cookies

[Jérôme Loyet]

Hi nginx dev,

for internal need, I wrote an upstream module which use a sticky
cookie to ensure a client is always sent to the same backend server.

All the loadbalancing intelligence stays in the
ngx_http_upstream_round_robin.c part of nginx core.

You can see the simple general algorithm in the following diagramm
http://nginx-sticky-module.googlecode.com/svn/trunk/docs/sticky.pdf

If you have time, can you review the code and see if I'm not doing
some stuff senselessly ?

Usage
	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];
	  - name:    the name of the cookies used to track the persistant
upstream server
		           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

You can try it by downloading the version 1.0-rc1 at
http://code.google.com/p/nginx-sticky-module/downloads/detail?name=nginx-sticky-module-1.0-rc1.tar.gz&can=2&q=

The project page is: http://code.google.com/p/nginx-sticky-module/

Thx
++ Jerome