Thank you Ondřej for the reply!

2. Read the olmMDBEntries from cn=monitor and make sure those stay in
sync

The olmMDBEntries help me out a lot! Thank you for this pointer. Since we already gather cn=monitor metrics, the data was already there so we just need to adjust our alerting for that.

The former gives you more information and is my go-to, but its use in
monitoring can be confusing: each serverID CSN has to be compared
independently, you cannot do straight time arithmetic for alerting, ...

Any tool recommendations for this?

Some of that is abstracted away by syncmonitor[0] which should be easy
to adapt for most monitoring solutions and can even do real-time
monitoring + alerting. It is under active development, most recently in
the textual branch to expose a TUI frontend and refactor the library to
track the cookies on a per-SID basis for real-time replication delay
measurement.

What is not "abstracted away by syncmonitor" ?

Best,

Dave