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We recently worked on a Rails application that had page and action caching set up, only to find that it was not actually working. It occurred to me that many Rails/Passenger/Apache applications may have caching set up in a way that it appears to be caching, when it is not actually caching. Searching through the interwebs for various Passenger/Apache configurations, such as this snippet on Github or this discussion on Google Groups, I found that many did not work with the most recent version of Phusion Passenger. What’s more, these configurations give the appearance that they are working.

For an introduction to caching with Rails, check out this post: Caching With Rails: An Overview

The Appearance That Caching Works

Here is what I mean by giving the appearance that caching is working:

1. you add caches_page :index to your controller, for example
2. configure and restart your server
3. load the index page
4. check your rails cache directory on your server, and see the index.html
5. it works! (hint: this step is wrong, you’re not quite there yet)

Just because Rails is generating your cached page does not mean that your server is subsequently serving the cached .html file instead of sending the request to Rails again.

Ensure It’s Serving the Cached Page

To make sure it’s subsequently serving the cached page, the easiest method is to look at the created date on the cached file on your server, for instance: