node-redis-pubsub | Simple pubsub for node using Redis | Runtime Evironment library

By default, socket.io connects with several consecutive http requests. It essentially starts in HTTP polling mode and then after some initial data exchange, it switches to a webSocket transport.

Because of this, a cluster that does not have any sort of sticky load balancing will not work. Each of the initial consecutive http requests that are all supposed to go to the same server process will probably be sent to different server processes in the cluster and the initial connection will not work.

There are two solutions that I know of:

1. Implement some sort of sticky load balancing (in the clustering module) so that each client repeatedly goes to the same server process and thus all the consecutive http requests at the beginning of a connection will go to the same server process.

2. Switch your client configurations to immediately switch to the webSocket transport and never use the HTTP polling. The connection will still start with an http request (since that's how all webSocket connections start), but that exact same connection will be upgraded to webSocket so there will only ever be one connection.

FYI, you will also need to make sure that the reconnect logic in socket.io is properly reconnecting to the original server process that is was connected to.

socket.io has node.js clustering support in combination with redis. While the socket.io documentation site has been down for multiple days now, you can find some info here and Scaling Socket.IO to multiple Node.js processes using cluster and here's a previously cached version of the socket.io doc for clustering.