Rails でサクッと Redis を Master/Slave 構成にする ref: http://qiita.com/eccyan/items/7a7bdeb693f4df16b8f9

redis.rb

class Redis
  class Client
    def call(command, &block)
      master_host = MASTER_HOST_URI
      slave_host  = SLAVE_HOST_URI

      # Slave に向けたいお好きなコマンドを登録
      slave_commands = [:get, :hget, :hgetall] 

      disconnect
      @options[:host] = if slave_commands.include?(command[0])
        slave_host 
      else
        master_host
      end
      connect

      reply = process([command]) { read }
      raise reply if reply.is_a?(CommandError)

      if block
        block.call(reply)
      else
        reply
      end
    end
  end
end