haproxy maxconn for nginx
Adds a request queue to Nginx that allows the limiting of concurrent requests
passed to the upstream.  "max_connections N;" in an upstream directive means
that each upstream server will be given N request at a time, per Nginx
worker. For example, if you have two workers and "max_connections 1;" then
there will be a total of 2 requests at a time on each upstream server.

Some benchmarks: http://four.livejournal.com/955976.html

Usage:

  upstream mongrels {
    server 127.0.0.1:8001;
    server 127.0.0.1:8002;
    max_connections 1;
  }

Install:

This module requires one to patch Nginx. The module also includes a Makefile
for easily building it into Nginx and running tests. If the Makefile is used
then the first line must be changed to point to the Nginx source tree. 
Here is an example of how one might compile nginx with this module.

  tar -zxf nginx-0.6.35.tar.gz
  tar -xzf ngx_max_connections-0.0.5.tar.gz
  cd nginx-0.6.35
  patch -p0 < ../ngx_max_connections-0.0.5/patches/nginx-0.6.35.patch
  cd ../ngx_max_connections-0.0.5
  vim Makefile #### edit the first line!
  make configure
  make
  make test    #### requires ruby, rubygems, rack, and httperf