So apparently Engine Yard has a patch for Nginx, called nginx-ey-balancer, to add a max_connections directive for connections being passed upstream.
The patch is to fix issues such as Mongrel backend servers being dropped by Nginx (at least, that's my understanding).

I searched the forums, though, didn't see any mention of it.

Is Igor aware of this patch, and is this needed in Nginx for anyone using the proxy module?
(Our backend is nginx+php-fpm, w/ nginx reverse proxy on frontend, and will be using the load balancer in the near future).

http://github.com/ry/nginx-ey-balancer

[quote]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;
}[/quote]