Using Redis as Rails Cache Store

The Redis database is often use for cache purpose with Rails deployments. Hence you might want to clear its content after each deployment. One solution could be to empty it in a postdeploy hook. Another solution can be to prefix the cache key with the build deployment ID provided by Scalingo.

The deployment ID is available in the SOURCE_VERSION during the build phase and CONTAINER_VERSION at runtime. More information about these variables.

With Ruby on Rails, configuring such cache is done using this single line:

config.cache_store = :redis_cache_store, { url: "#{ ENV['REDIS_URL'] }/0:#{ ENV['SOURCE_VERSION'] || ENV['CONTAINER_VERSION'] }" }

By default, Redis databases on Scalingo have a timeout.

If you don’t want to depend on the timeout of the server, you may want to change the client connection timeout. You can do it like this:

config.cache_store = :redis_cache_store, { url: "#{ ENV['REDIS_URL'] }/0:#{ ENV['SOURCE_VERSION'] || ENV['CONTAINER_VERSION'] }", timeout: 30 }

If you want an automatic reconnection after the connection timed out, you should set the reconnect_attempts option:

config.cache_store = :redis_cache_store, { url: "#{ ENV['REDIS_URL'] }/0:#{ ENV['SOURCE_VERSION'] || ENV['CONTAINER_VERSION'] }", timeout: 30, reconnect_attempts: 1 }

This simple trick will automatically invalidate the cache after each successful deployment. You’d certainly also want to enable Redis cache mode on its Dashboard on Scalingo to avoid filling your Redis database completely and tell Redis to drop old and unused keys.


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