[kevinfat]

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?

[jabr]

All this change in nginx does is allow WebSocket connections to be proxied, so your questions don't really make sense. WebSocket's work like TCP sockets, and your backend server still needs to manage the socket directly. For example, Unicorn is not a WebSocket server, though there are WebSocket-capable servers derived from Unicorn (e.g. http://rainbows.rubyforge.org/).

If your backend dies or drops the connection, the WebSocket closes, and the client will have to reconnect. If it was just dropped, you can use nginx's ip_hash proxy option to send the reconnect to the same backend server, but it would be a new WebSocket, and the client/server will have to recreate the session state.