Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy(open Source). You install it in front of any server that speaks HTTP and configure it to cache the contents.
Varnish Cache Portfolio
Varnish is used by high-profile, high-traffic websites including online newspaper sites such as The New York Times, The Guardian, The Hindu, Corriere della Sera, social media and content sites such as Wikipedia, Facebook, Twitter, Vimeo, and Tumblr. Of the Top 10K sites in the web, around a tenth use the software. - Source WiKi.
How to install please click here:
https://www.varnish-cache.org/docs/trunk/tutorial/
Varnish Server Flexibility
One of the best features we came across in Varnish Cache, in addition to it's performance, is the flexibility of it's configuration language, VCL. VCL enables you to handle the HTTP requests the way you want, what to cache, how to cache it, modifying HTTP headers etc. etc.