A question about image hosting and docker

This is something I've been meaning to "get around to" for a very long time, and I got quite excited seeing a recent discussion about Immich. And I looked at the various docker-compose files for Immich, and for Piwigo, PiGallery2, and PhotoPrism. Immich seems to require a number of different containers, whereas the others seem much simpler. That is to say, the docker-compose file for Immich seems very complicated.

Is this, in fact, an issue? Maybe I'm simply worrying about something which is not a problem.

And for a more generic question: for software that requires a database (as all image hosting does), do I need to start a new instance of MariaDB (for example), or can I use the database engine that's been set up in another container? That is, can I have one running instance of a database serving the needs of several different containers?

Thanks heaps, folks.