Install Docker Compose, then:
$ docker-compose up -d
And then point your browser to http://localhost:3000.
This will start four Socket.IO nodes, behind a nginx proxy which will loadbalance the requests (using the IP of the client, see ip_hash).
Each node connects to the redis backend, which will enable to broadcast to every client, no matter which node it is currently connected to.
# you can kill a given node, the client should reconnect to another node
$ docker-compose stop server-george