I ought to try syncrepl before talking too much, but anyway:
Quanah Gibson-Mount writes:
It sounds like it gracefully solves the ability of keeping both
and replica configurations around for the most part. What still
remains sticky is ACLs. There are plenty of valid reasons for the
master to have very different ACLs than the replicas do.
And things like <authz-policy> and <allow>. Security settings, if you
run a master inside a well protected subnet and partial slaves on more
Master and slave can share some but not all databases, and you might
want to replicate config of those they share - but this way the database
numbers will differ. Might not share all related schema either.
<threads>, cache settings, <argsfile>, etc. if your servers run on
different OSes. Which can be useful so that if an OS-specific problem
hits one server, others are in no danger.
I'm sure there are good reasons for plenty of other things to differ,
while config-replication could still be useful. Depends on how flexible
partial config-replication is intended to be.