“Varnish can do a lot of things, but it's mostly known as a reverse HTTP proxy. It brands itself as an HTTP accelerator, making HTTP requests faster by caching them.

It can also serve as a TCP load balancer (using pipe in the VCL code, more on that later), an HTTP load balancer or a generic reverse proxy.

It uses the Varnish Configuration Language (VCL) to allow you as a developer or sysadmin to modify the behaviour of Varnish and to play with the HTTP protocol to shape it so it behaves the way you want.”