Load Balancing & QoS with HAProxy

[Ed: and seems that nginx can be used like an proxy and load balancer , what next ? you can get rid of complex lvs ]

Did you know that Flickr optimizes all of their pages to render in sub 250ms?

When you're fighting with response times, the worst thing you can possibly do is queue up another request behind an already long running process. Not only does the first request take forever, but everyone else must wait in line for it to finish as well! To mitigate the problem HAProxy goes beyond a simple round-robin scheduler, and implements a very handy feature: intelligent request queuing!

HAProxy Request Queuing

You can get similar functionality in Nginx directly with the 'Fair Proxy Balancer' plugin (EngineYard is rumored to be running it).