Note that if your websocket server logic runs on nodejs with socket.io, you can tell socket.io to use a shared redis key/value store for synchronization. This way you don't even have to care about the load balancer, events will propagate among the server instances.
var io = require('socket.io')(3000);
var redis = require('socket.io-redis');
io.adapter(redis({ host: 'localhost', port: 6379 }));
See: socket.io/docs/v4/using-multiple-nodes/
But at some point I guess redis can become the bottleneck...
