How to implement instant messaging system in mobile apps if firebase is not suitable?

Question

Mobile development

Hello.
Previously, I faced the need to implement instant messages in a mobile application (a simple messenger) and used realtime database from firebase for this. Now the task is to add a messenger for users to the finished application, only the application server is a regular server with a regular relational database, so it will be very difficult to cram firebase into this whole thing. In this regard, a few questions:
1. Are sockets used for these purposes?
2. What exactly to google on this topic? Maybe there are some ready-made services that will simplify the solution of this task?
3. More interested not in the case of "how to do it ideally", but in order to get an acceptable result for a relatively small amount of effort. Or will it not work?
I would be very grateful for any information on this matter.

Answer 1

Use websockets or long pooling, well, any language for server-side development