Just a quick head up with bunch of links about Varnish integration for symfony.
I’m sure you have heard of Varnish reverse proxy server
Varnish is a web accelerator written with performance and flexibility in mind. It’s modern architecture gives it a significantly better performance than many of it’s competing products. Varnish store web pages in memory so the web servers don’t have to create the same web page over and over again. The web server only recreate a page when it is changed. Additionally Varnish can serve web pages much faster then any application server is capable of – giving the website a significant speed up.
So in first order you may be interested to integrate Varnish to handle pages which don’t require authentication (for myself I’m still not sure if there is any advantage for integrating pages for logged in users):
http://snippets.symfony-project.org/snippet/365 (Controlling HTTP Caching (Squid, Varnish, ..) with cache.yml files)
http://symfony.com/doc/2.0/cookbook/cache/varnish.html (Varnish in Symfony2)
http://stackoverflow.com/questions/3833703/using-varnish-in-a-symfony-application (Solo question with varnish rule which can be re-used)
http://groups.google.com/group/symfony-users/browse_thread/thread/435b0c7dd787a24c (Using Varnish Cache with Symfony)
http://www.symfony-project.org/plugins/sfHttpHeaderCachePlugin – plugin which serves the response with valid caching headers