Varnish is a webcache & http accelerator. Varnish will either serve cached content, or retireve content from the server, and cache it. Varnish will reduce I/O pressure from webservers.
Configuration is controlled by /etc/varnish/default.vcl
Any traffic pointed at port 8080 will be through varnish.
To start varnish immediately:
#rc-service varnishd start
To start varnish at boot:
#rc-update add varnishd default
To verify that your traffic is going through varnish.
$curl -I https://www.varnish-cache.org/