So in practical terms how does one setup backends to use WebSockets. For example, suppose you have nginx in front of a bunch of Unicorn or Rainbow processes and there are two clients that have made websocket connections. Consider a chat application. One of them sends a websocket message and the backend that receives it needs to push the message along the other websocket connection. But how does it know which backend to forward to? What is the intended idiomatic way of maintaining the necessary state?