In this DigitalOcean article, as a part of a series to help developers with scaling, we will be talking about configuring Varnish with Drupal. This will greatly reduce the amount of time it takes users to load your Drupal based website, and increase t

Source: How To Configure Varnish for Drupal with Apache on Debian and Ubuntu | DigitalOcean

So I recently setup Varnish on my web servers and it has vastly sped up my sites. However it also broke several things on my Drupal based sites. I ran across this article while trying to kill bugs and it fixed me right up.