socket.io broadcast function & Redis pub/sub architecture

Question

i would appreciate if somebody could help me with a small doubt.

Whats the difference between using socket.io broadcast function and designing the architecture with pub/sub on Redis?.

For instance, on the further example, the node.js server is listening (socket.io) CRUD requests (create) for a "key" (model 'todo'), and value 'data'. The moment it receive it, it emits again to the same user, and broadcast to all users listening on the same "channel".

socket.on('todo:create', function (data, callback) {
    var id = guid.gen()
      , todo = db.set('/todo/' + id, data)
      , json = todo._attributes;

    socket.emit('todos:create', json);
    socket.broadcast.emit('todos:create', json);
    callback(null, json);
});

But there is another way of "broadcasting" something using socket.io, and is using a pub/sub platform with Redis for key:value functions. For instance, on the further case, we are listening for a CRUD request based on a "key" (model), function (create), and value (data). But on this case, once its received, is not sent via "socket.broadcast.emit()", but published on Redis:

socket.on(key + ':create', function (data, callback) {
  var t = new ModelClass(data)
    , name = '/' + key + ':create';
  t.save(function (err) {
    pub.publish(key, JSON.stringify({key: name, data: t}));
  });
});

So on the server side, every change made on a model (and published to Redis), will be catched up (handler), and sent to the user client side (on my case, backbone.js), that will render its model according to the key:value received:

sio.on('connection', function (socket) {

   sub.on('message', function (channel, message) {
      var msg = JSON.parse(message);
      if (msg && msg.key) {
          socket.emit(msg.key, msg.data);
      }
});

So my question is very simple :-) : whats the difference of both architectures? which one is more scalable? better design? mode advance?

It looks to me that the pub/sub architecture is suitable for platforms that doesn't support 'realtime' naturally, like Ruby, in contrast to Node.js, that supports it natively.. Am i wrong?

Answer 1

Socket.io's broadcast method will broadcast to all the sockets that are connected to the current Node.js server, but what if your application becomes popular and you need more than one server to host all the socket.io connections? Using Redis' Pub/Sub your messages can be distributed to many servers at once.