I wondered about that myself these days and decided to give each stack its own db. Makes it easier to throw a stack into the bin without having to manually prune the associated databases. I might end up running a database container anyways for tests and side projects and things like that but service stacks get their own db of their choice.

The cost of running a db container for each stack is negligible compared to the comfort of not having to clean up your main database container after you just tried some random container. Then you also have different requirements by different containers, each asking for a specific database for whatever reason and lastly you have another level of seperation between your services

1 db per stack. Not worth your time to secure, configure and debug one big db.

One database for many different services could pose a security risk, though it should be extremely low if each service can access only its own database. However, it'd be harder to distribute services across different hosts if you ever decided to do that. Also, different services could require or work better with different database types. I prefer to use separate database containers.

Unless you are very constrained on resources, using a database per application is much easier.

I agree with the posts above. Db per stack/service.

They are cheap, disposable, ring fenced from causing issues with other dB's, exact version that has been tested on.

The list is endless. We'll, I'm at my end.

Oo. Typically compose has everything you need prewritten including the db.

Not only do I prefer separate db for each stack, ideally the db and app are in the same container. Fewer containers to manage and makes the app nice and self-contained.

Backup / restore gets complicated if you have multiple apps in 1 dB