ey-balancer?

[Ryan Dahl]

There were many people running nginx -> haproxy -> mongrels just for
haproxy's request queueing functionality. It turns out that if you
have slow or chaotic response times from backends (often the case in
Rails world) queuing requests in the proxy will tighten up the
response time variance dramatically, getting the tail-end latency
under control. I'm not sure how many people are using it, but it is
being used on at least a few production sites. It's more or less
stable.