Howtoforge shows you how to put Varnish in front of Apache on Ubuntu/Debian

Varnish is an open source "web accelerator" which you can use to speed up your website. It can cache certain static elements, such as images or javascript but you can also use it for other purposes such as Loadbalancing or some additional security. In this tutorial we will focus on the latter one.In this mode, Varnish will stop incomplete HTTP requests from reaching your Apache webserver.

  Putting Varnish In Front Of Apache On Ubuntu/Debian