This is Varnish Cache, a high-performance HTTP accelerator.
Varnish Cache stores web pages in memory so web servers don’t have to
create the same web page over and over again. Varnish Cache serves
pages much faster than any application server; giving the website a
significant speed up.
Documentation wiki and additional information about Varnish Cache is
available on: https://www.varnish-cache.org/
