[cryptonector]

There are no standard mechanisms for keeping heterogeneous databases in sync, or even DBs of the same types but with different schemas.

The standard thing to do is to have a source of truth, as described in various comments here like https://news.ycombinator.com/reply?id=22690991&goto=item%3Fi...

Sometimes you'll have multiple sources of truth for (hopefully non-overlapping) subsets of the data in question.

These things are messy. You have to do the hard work of writing sync tools. You want sync tools that work off of incremental / delta feeds, but you also need (slower) tools that can make-it-right based on the totality of your data -- at least the first time you sync two systems, and often also for auditing purposes to make sure that the incremental (fast) sync is working correctly.