redis-store’s redis-rails gem is awesome, but it can be a pain in the buttox to get configured on Heroku.

That’s because Heroku’s ever-growing list of Redis providers all use config vars to set the Redis URL and redis-rails expects you to hook up the cache store and session store during the Rails application boot process, during which the config vars are unavailable.

Here’s how I got it working:

First, delete config/initializers/session_store.rb. It’s not needed because we’ll initialize the session store and the cache store in the same place.

Next, create config/initializers/redis_store.rb and put this in it:

redis_url = ENV["REDISCLOUD_URL"] || "redis://"
MyApp::Application.config.cache_store = :redis_store, redis_url
MyApp::Application.config.session_store :redis_store, redis_server: redis_url

That’s all there is to it! A few notes:

  1. initializers are executed after application.rb, at which point Heroku’s config vars are available
  2. when the config var URL is nil, like in dev mode, it will revert to your local Redis server
  3. I’m using RedisCloud as a Redis provider, but you’ll need to adjust the config var to match whichever provider you choose
  4. Be sure to replace MyApp with the name of your app ;)
  5. The /myapp at the end of the fallback URL is optional. It adds a namespace to all Redis keys. I like this in dev mode because I can see all of my app’s keys by doing a keys myapp* in the Redis CLI. Feel free to omit

Happy caching!