HAProxy is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications. It is particularly suited for web sites crawling under very high loads while needing persistence or Layer7 processing

Performance Parameters of Haproxy:

maxconn <number>
  Sets the maximum per-process number of concurrent connections to <number>. It
  is equivalent to the command-line argument "-n". Proxies will stop accepting
  connections when this limit is reached. The "ulimit-n" parameter is
  automatically adjusted according to this value. See also "ulimit-n". … Read the rest

…in other words, don’t implement in extra complexity if you don’t need it. A site handling a few thousand requests per day will do fine on a default configuration and just about any hardware. This article is geared towards a site that needs to handle multiple concurrent requests [ten to several hundred per second].

General [in order of importance]

RAM

The single biggest issue affecting webserver performance is RAM. Have as much RAM as your hardware, OS, and funds allow [within reason].

The more RAM your system has, the more processes [and threads] Apache can allocate and use; which… Read the rest