HA-Proxy

HA-Proxy is a TCP/HTTP reverse proxy which is particularly suited for high
availability environments. Indeed, it can:
 - route HTTP requests depending on statically assigned cookies
 - spread the load among several servers while assuring server persistence
   through the use of HTTP cookies
 - switch to backup servers in the event a main one fails
 - accept connections to special ports dedicated to service monitoring
 - stop accepting connections without breaking existing ones
 - add/modify/delete HTTP headers both ways
 - block requests matching a particular pattern
 
 It needs very little resource. Its event-driven architecture allows it to easily
 handle thousands of simultaneous connections on hundreds of instances without
 risking the system's stability.