feedback: Monitoring a replica set | Tarantool

<…>istics for the
other two masters, given in regard to master #1.
|The primary indicators of replication health| are:

idle, the time (in seconds) since
the instance received t<…>

https://www.tarantool.io/en/doc/latest/book/replication/repl_monitoring/

Am I understand right: replication idle and replication lag are the same except that replication lag tracks only WAL writes and is not updated with heartbeats?

On https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_info/replication/ I see that both lag and idle are in the upstream object (on replica), but the downstream object (on master) has only idle.

To be honest, the documentation does not give me a predicate, which I should use to decide, whether an instance is healthy. It also does not reveal details how exactly given two metrics work, so I can't construct this predicate myself.

(Filed by @Totktonada.)

Start by reading the replication monitoring page and the box.info/replication reference linked in the issue, comparing the upstream and downstream metric descriptions. Done means the documentation explains how idle and lag differ, how heartbeats affect them, and provides a clear predicate for deciding whether a replica set instance is healthy.