Today my friend Patrick Crowley and I were talking about scaling his website: http://cinematreasures.org since an article covering his work will soon be published in a very popular newspaper. Patrick’s site is hosted on Heroku which comes by default with Varnish caching enabled. The challenge is that a lot of people using the Rails framework are used to doing page caching instead of relying on HTTP caching, even though this feature was added a long time ago. The major problem with page caching is that it doesn’t scale that well as soon as you run more than one server. Indeed you would need to store the page content to a shared drive between your servers or use memcached and do some work to avoid hitting your app every single time. On the other hand, HTTP caching is extremely easy to handle at the application level and it will dramatically reduce the amount of requests hitting your app. Let me explain a little more about HTTP caching.