Redis cluster stores for ActiveSupport

This gem is an extension to redis-activesupport that adds support for a few features required to use redis-store with redis cluster. Right now there isn't an official redis cluster client in ruby, so it's become common to use a redis cluster proxy like corvus. When switching there are a few things you can't do with redis cluster that you can do with a single redis server. Most of them revolve around issuing commands with multiple keys. In redis cluster, your keys are partitioned and live on different physical servers, operations like KEYS are not possible. Corvus will break apart MSET and MGET into individual GET and SET commands automatically, but in general, it's not a good idea to use them.

Usage

This gem is a small extension to redis-activesupport, so refer to their documentation for most configuration. Instead of specifying :redis_store you must now specify :redis_cluster_store to load this extension.

module MyProject
  class Application < Rails::Application
    config.cache_store = :redis_cluster_store, options
  end
end

Additionally, there's a new configuration option: :ignored_command_errors. This is useful if you're using a redis cluster proxy like corvus who will raise a Redis::CommandError with a message indicating the cluster is offline or experiencing a partial outage. This extension allows you to whitelist certain ignored_command_errors that would normally be raised by redis-activesupport. By default this gem whitelists the following errors:

DEFAULT_IGNORED_COMMAND_ERRORS = ["ERR Proxy error"]

If you need additional errors added to the whitelist, you can do this through your own configuration or open a pull request to add it to the default whitelist. NOTE: this list is turned into a Set to keep lookups fast, so feel free to make this list as big as you need. Example:

module MyProject
  class Application < Rails::Application
    config.cache_store = :redis_cluster_store, {:ignored_command_errors => ["Uh oh", "Please, stop", "Fire emoji"]}
  end
end

With this change, your cache store will now silently fail once again so a redis cluster won't knock your rails apps offline.

Installation

Add this line to your application's Gemfile:

gem "redis-cluster-activesupport"

And then execute:

$ bundle

Or install it yourself as:

$ gem install redis-cluster-activesupport

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/film42/redis-cluster-activesupport.

License

The gem is available as open source under the terms of the MIT License.