Question

I’m using CloudFlare CDN on my Rails 3.1 application. Cloudflare is a CDN that works at the DNS level. On the first hit to a static asset, CloudFlare loads it from your app then caches it in their CDN. Future requests for that asset load from the CDN instead of your app.

The problem I’m having is that if you set controller caching to true:

config.action_controller.perform_caching = true

it enables the Rack::Cache middleware. Since Rails sets a default cache control setting for static assets, those assets get written to the Rails.cache store. As a result my cache store (in my case redis) is being filled up with static assets with the url as the hash key.

Unfortunately, I can’t turn off the static asset cache control headers without affecting how Cloudflare and my users’ browsers cache the assets. I can’t turn off controller caching or I lose page/action/fragment caching. Same result if I delete the Rack::Cache middleware.

Does anyone have any other ideas?

Update: I’ve opened a ticket on GitHub here.

Answer 1

The original poster wanted to prevent static assets from getting into the general Rails cache, which led them to want to disable the Rack::Cache. Rather than doing this, the better solution is to configure Rack::Cache to use a separate cache than the general Rails cache.

Rack::Cache should be configured differently for entity storage vs meta storage. Rack::Cache has two different storage areas: meta and entity stores. The metastore keeps high level information about each cache entry including HTTP request and response headers. This area stores small chunks of data that is accessed at a high frequency. The entitystore caches the response body content which can be a relatively large amount of data though it is accessed less frequently than the metastore.

The below configuration caches the metastore info in memcached but the actual body of the assets to the file system.

Using memcached gem:

config.action_dispatch.rack_cache = {
  :metastore    => 'memcached://localhost:11211/meta',
  :entitystore  => 'file:tmp/cache/rack/body',
  :allow_reload => false
}

Using dalli gem

config.action_dispatch.rack_cache = {
  :metastore    => Dalli::Client.new,
  :entitystore  => 'file:tmp/cache/rack/body',
  :allow_reload => false
}

By the way this configuration is the recommendation for Heroku:
https://devcenter.heroku.com/articles/rack-cache-memcached-static-assets-rails31