A client of mine used some SaaS from a vendor. The vendor sold you an “Instance“ that basically is an EC2 instance. Each instance has a self-contained app and self-contained database. Migration and app update are handled a single client/single instance at a time. Standard backup and restore tools can be used. It’s a more expensive approach but the software was specialized and expensive too. An upside of this model, it lends itself well to clients who require on-premise deployment. And it seems for heavy use clients, you can scale up their instance and database as needed.