I don't mind having server_id=1 by default; we just need to update documentation and probably provide instructions about steps which make sure that particular instance is not part of replication (if DBA want that and we want such feature) https://github.com/MariaDB/server/commit/1c91569 , (plus fix MDEV-12597)

Please find out where the change came from. I remember monty wanted to change the default, and it made sense, but I don't believe that's quite what was it meant to be. I think it should be the hard default that's changed – it makes no sense to set it to 0, then complain about it and adjust it to 1. And if it's set to 0 explicitly, it should be preserved.

In provided commit and current tree indeed I see that default is adjusted to 1 as well, but probably it gets overwritten somewhere else:

-       VALID_RANGE(0, UINT_MAX32), DEFAULT(0), BLOCK_SIZE(1), NO_MUTEX_GUARD,

+       VALID_RANGE(1, UINT_MAX32), DEFAULT(1), BLOCK_SIZE(1), NO_MUTEX_GUARD,

It is not printed for me " without server-id configured". You probably have this server_id=0 in some my.cnf .Could you check?

Yeah you are right - my fault - somehow I overlooked that dealing with many issues at the same time. I've asked Ian to address this in 10.2 documentation, will close the bug once documentation is fixed

The change of default has been documented