chat-app-server | end server for chat application built using express | Socket library

I haven't used Socket.IO before, so I may be off base, but from a quick read of the docs, it seems like things should just work.

Two points from the docs:

a.) When using WebSockets, this is a non-issue. Cloud Foundry fully supports WebSockets. Hopefully, most of your clients can do that.

b.) When falling back to long polling, you need sticky sessions. Cloud Foundry supports sticky sessions out-of-the-box, so again, this should just work. There is one caveat though regarding CF's support of sticky sessions, it expects the session cookie name to be JSESSIONID.

Again, I'm not super familiar with Socket.IO, but I suspect it's probably using a different session cookie name by default (most things outside of Java do). You just need to change the session cookie name to JSESSIONID and sticky sessions should work.

TIP: you can check the session cookie name by looking at your cookies in your browser's dev tools.

Final note. You don't need Nginx here at all. Gorouter, which is Cloud Foundry's routing layer, will handle the sticky session support for you.