In the setup described here (it has changed a bit in the 6 months since this article was written) Varnish was being used primarily for caching and sending neede

In the setup described here (it has changed a bit in the 6 months since this article was written) Varnish was being used primarily for caching and sending needed requests to the single application server. Calling it a load balancer at that point was a simple misnomer. Today we still have Varnish at the front of our stack for caching and also use it as a load balancer for a handful of application servers.