Im curious for anyone who has done this: what’s the point of going all the way from one-db to one-db-per-customer? Why not just split the customers to 2 databases, then to 3, etc? Seems like the same level of system complexity but you avoid the lots-of-databases scaling problem.

You probably don’t even need to be able to migrate people between shards… just put everyone on one db until you hit 50% utilization, then spin up a fresh db and put all new customers on that one. Repeat whenever you run out of databases under 50%.