Varnish Cache is a modern reverse proxy cache software package. It has been built from the ground up to be a dedicated reverse proxy cache so it doesn't have legacy functionality and code, making it blazing fast. It is supported on Linux and FreeBSD and is included in most popular distributions

Drupal Modules that interact with Varnish Varnish Module integrates Drupal to Varnish over the Varnish administration interface. It can purge URLs from the proxy cache using regular expressions and can display varnish statistics. Purge Module just implements purging over HTTP together with the Expire Module https://ftp.drupal.org/files/projects/varnish-7.x-1.10.tar.gz

GitHub Link: 
https://github.com/backdrop/backdrop-issues/issues/6164
GitHub Issue #: 
6164