Socket.io and multiple Dyno's on Heroku Node.js app. WebSocket is closed before the connection is established

Question

I'm building an App deployed to Heroku which uses Websockets.

The websockets connection is working properly when I use only 1 dyno, but when I scale to >1, I get the following errors

POST http://****.herokuapp.com/socket.io/?EIO=2&transport=polling&t=1412600135378-1&sid=zQzJJ8oPo5p3yiwIAAAC 400 (Bad Request) socket.io-1.0.4.js:2

WebSocket connection to 'ws://****.herokuapp.com/socket.io/?EIO=2&transport=websocket&sid=zQzJJ8oPo5p3yiwIAAAC' failed: WebSocket is closed before the connection is established. socket.io-1.0.4.js:2

I am using the Redis adaptor to enable multiple web processes

var io = socket.listen(server); var redisAdapter = require('socket.io-redis'); var redis = require('redis');  var pub = redis.createClient(18049, '[URI]', {auth_pass:"[PASS]"}); var sub = redis.createClient(18049, '[URI]', {detect_buffers: true, auth_pass:"[PASS]"} );  io.adapter( redisAdapter({pubClient: pub, subClient: sub}) ); 

This is working on localhost (which I am using foreman to run, as Heroku does, and I am launching 2 web processes, same as on Heroku).

Before I implemented the redis adaptor I got a web-sockets handshake error, so the adaptor has had some effect. Also it is working occasionally now, I assume when the sockets match the same web dyno.

I have also tried to enable sticky sessions, but then it never works.

var sticky = require('sticky-session'); sticky(1, server).listen(port, function (err) {   if (err) {     console.error(err);     return process.exit(1);   }   console.log('Worker listening on %s', port); }); 

Answer 1

I'm the Node.js Platform Owner at Heroku.

WebSockets works on Heroku out-of-the-box across multiple dynos; socket.io (and other realtime libs) use fallbacks to stateless processes like xhr polling that break without session affinity.

To scale up socket.io apps, first follow all the instructions from socket.io:

• http://socket.io/docs/using-multiple-nodes/

Then, enable session affinity on your app (this is a free feature):

• https://devcenter.heroku.com/articles/session-affinity

Answer 2

I spent a while trying to make socket.io work in multi-server architecture, first on Heroku and then on Openshift as many suggest.

The only way to make it work on both PAAS is disabling xhr-polling and setting transports: ['websocket'] on both client and server.

On Openshift, you must explicitly set the port of the server to 8000 (for ws – 8443 for wss on socket.io client initialization, using the *.rhcloud.com server, as explained in this post: http://tamas.io/deploying-a-node-jssocket-io-app-to-openshift/.

Polling strategy doesn't work on Heroku because it does not support sticky sessions (https://github.com/Automattic/engine.io/issues/261), and on Openshift it fails because of this issue: https://github.com/Automattic/engine.io/issues/279, that will hopefully be fixed soon.

So, the only solution I found so far, is disabling polling and use websocket transport only.

In order to do that, with socket.io > 1.0 server-side:

var app = express(); var server = require('http').createServer(app);  var socketio = require('socket.io')(server, {   path: '/socket.io-client' }); socketio.set('transports', ['websocket']); 

client-side:

var ioSocket = io('<your-openshift-app>.rhcloud.com:8000' || '<your-heroku-app>.herokuapp.com', {     path: '/socket.io-client'     transports: ['websocket'] }) 

Hope this will help.