Actually the reason I'm not caching more is due to a bug in Rack. https://github.com/rack/rack/pull/157 Rack seems to not handle session cookies correctly, they are always there even when there is no session set. Varnish does not cache things that sets cookies. (e.g pages where you are logged in, like a admin panel).

This makes things served through my sinatra application/unicorn have session cookies, even if it's something like a css file. I'm specifically stripping them out at this point but it shouldn't be needed. I don't know enough about Rack yet to fix the bug myself and way too busy with exams anyway.