MockRedis

A gem to make it easy to use different Redises for different things.

Getting Started

RedisSelector is a module that provides the #with_redis method.

#with_redis takes a string and a block, and calls the block with a connected Redis object. The connection is closed after the block exits.

The string is used to indicate what logical thing you're using Redis for. This allows for easy addition of new Redis servers if your data set starts getting too big.

Example:

class Competitor < ActiveRecord::Base
  extend MockRedis

  def self.top10
    with_redis('leaderboards') do |redis|
      redis.zrange(LEADERBOARD_KEY, 0, 9).map {|id| self.find(id)}
    end
  end
end

class BlogPostsController < ApplicationController

  def create
    # ...
    with_redis('blog_posts') {|r| r.incr('blog_posts_created' }
    render
  end
end

By default, both these calls will connect to the same Redis. Now, let's say your leaderboard data is getting really big, and it's taking up too much space on your one little Redis machine. You spin up a new one and tell RedisSelector about it:

RedisSelector.configure(
  'leaderboards' => {'host' => 'big-huge-redis-box'}
  # default is localhost for things not mentioned here
)

Then, Marketing goes crazy and starts posting blogs all over the place, and all your blog posts start taking up a ton of space.

RedisSelector.configure(
  'leaderboards' => {'host' => 'big-huge-redis-box'}
  'blog_posts'   => {'host' => 'other-redis-box'}
  # default is localhost for things not mentioned here
)

That's the only code change you have to make. Throw that in config/environments/production.rb and you're done. In development, you probably haven't bothered to set anything up, so everything will just go to localhost.

You can get separation by using different Redis databases, too. For example, if two different models use the same Redis keys and step on each other, you can split them up like so:

RedisSelector.configure(
  'model1' => {'host' => 'redis-box', 'db' => 1}
  'model2' => {'host' => 'redis-box', 'db' => 2}
  # default is localhost/0 for things not mentioned here
)

Since they're in different databases, they get their own keyspaces and don't step on each other.

Testing

RedisSelector supports the use of MockRedis in test mode. Add mock_redis to your Gemfile, and call RedisSelector.mock!.