How to make signal server for peer-to-peer?

Question

Spring

I have a messenger app that works on a peer-to-peer basis. I have a central server with a database of registered users and logic. Everything works fine on the local network. It does not pass through NAT, of course. I add clients and they now recognize their ports and ip through the public STUN server. But how do they know the address where to send them? Plus, they change every time. I read: the signal server is necessary. The question is how best to implement this signaling server. Can it be done in the same application as the central one with logic? Or is it better separately (by the way, maybe there are some features in it?)? There will be video broadcasts and I would like to save on hosting and traffic. As I understand it, for each packet with bytes it will re-apply to the signal one during the entire broadcast? Maybe,

If important, I use java and spring.

Thank you if anyone can help