Cache-Control: max-age header missing from static files in Drupal
One of the sites I maintain recently had a server upgrade to Ubuntu 14.04.4, which included a new version of varnish (version 3.05) which required an update to the Varnish configuration. After setting up a new default.vcl file I was monitoring the headers sent and received to make sure that what was supposed to be cached was in fact being cached by Varnish. While testing I discovered that I was not getting any Cache-Control headers from static files like images.