Graceful replication shutdown

[kickster97]

WHAT is this pull request doing?

Wait for followers to be in sync before closing server.

HOW can this pull request be tested?

run specs for #close

[viktorerlingsson]

LGTM 👍

A couple of questions;

Do we stop publishers to leader somewhere? Or can this keep going "forever" if you keep publishing? Maybe that is done by the server earlier when initiating shutdown?

Should there be some kind of timeout on the sync? I don't see anything like that in this code. Maybe we should let that be handled outside of LavinMQ though

[spuun]

Do we stop publishers to leader somewhere? Or can this keep going "forever" if you keep publishing? Maybe that is done by the server earlier when initiating shutdown?

Replication is closed last, so vhost should have closed all client connections before (and shovels/federations).

Should there be some kind of timeout on the sync? I don't see anything like that in this code. Maybe we should let that be handled outside of LavinMQ though

Yes, timeout or similar will probably be part of #547.