> There was a handful of new data that had been created in the intervening ~30 minutes. We pulled that diff data manually, and uploaded it to the new database.

But doesn’t that mean you had some partial downtimes? How did you manage to keep everything running during these 30 minutes where data was copied from the old DB to the new one? Let’s say there is a cron job that must be executed and its result would be stored back to the DB. Did you “pause” everything and reschedule it in the new instance once the diff copy was over?