Are WebSocket connections persistent to a single backend? That is, suppose Nginx is in front of two Unicorn processes.

Will Nginx maintain a mapping table of client browser connection to Unicorn process, so that messages will always hit the same Unicorn process? Does that mean the Unicorn processes don't behave in a "stateless" manner?

Then what happens to the websocket if a Unicorn process dies and is restarted? What does the client browser do? What does Nginx do? What happens to the websocket connections if Nginx dies and there is a failover to a backup Nginx instance?