example of subscribing incoming websocket connections to redis using eventmachine

websocket-server.rb

require 'rubygems'
require 'eventmachine'
require 'em-websocket'
require 'json'
require 'em-hiredis'

EventMachine.run do
  
  @channel = EM::Channel.new

  @redis = EM::Hiredis.connect
  puts 'subscribing to redis'
  @redis.subscribe('ws')
  @redis.on(:message) do |channel, message| 
    puts "redis -> #{channel}: #{message}"
    @channel.push message 
  end
  
  EventMachine::WebSocket.start(:host => '0.0.0.0', :port => 8080) do |ws|
    puts 'Establishing websocket'
    ws.onopen do
      puts 'client connected'
      sid = @channel.subscribe do |msg|
        puts "#{msg} -> backbone"
        ws.send msg
      end
      ws.onclose do
        puts 'client disappeared'
        @channel.unsubscribe(sid)
      end
    end
  end
end