Not quite the same, unless I'm misunderstanding. I'm talking about an online migration on a single RDS instance with an engine switch handled fully behind the s

Not quite the same, unless I'm misunderstanding. I'm talking about an online migration on a single RDS instance with an engine switch handled fully behind the scenes. The link provided doesn't seem to handle data changes since the snapshot, and also requires a switch in the application to point to the new instance which has been restored via snapshot. DMS gets closer than the above link, I think, since it will handle replication onto the target database for you. But, for two fully compatible database engines, it seems like you should be able to make the switch without having to fuss with replication configuration or spinning up a new instance at all.