As seen on varnish-misc@varnish-cache.org:

I read one web testimony of a person who used Varnish to scale a site up to almost 200 million page views a month.

I’d like to find someone who has that level of expertise.

At work we have a Varnish cluster which, during the month of March, served over 17 billion requests for an average of 6,400 requests/second.

This cluster contains two physical machines with 24 cores and 192GB of RAM apiece. These machines have tons of spare capacity; their load average peaked at approximately 4. We’ve even considered virtualizing the cluster.

Varnish is a pretty amazing piece of software.