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_store, "#{ ENV['SCALINGO_REDIS_URL'] }/0/cache:#{ ENV['SOURCE_VERSION'] || ENV['CONTAINER_VERSION'] }", {expires_in: 1.hour}

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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