If I have several backends that more or less depend on each other anyway (for example: Lemmy + pict-rs), then I will create separate databases for them within a single postgres - reason being, if something bad happens to the database for one of them, then it affects the other one as well anyway, so there isn’t much to gain from isolating the databases.

Conversely, for completely unrelated services, I will always set up separate postgres instances, for full isolation.

This is already implemented in lemmy 0.18.1 for comments and posts!

I just want to point out that you don’t need to use neither Docker nor nginx to run Lemmy.

At the end of the day, the really required pieces are:

1. lemmy_server binary
2. Lemmy-ui
3. pict-rs binary
4. PostgreSQL database

How you get those things to talk to each other is totally up to you. There’s nothing stopping you from just using Apache as a reverse proxy, for example.

One possible Dockerless setup is described here: https://join-lemmy.org/docs/en/administration/from_scratch.html. This should give you some idea of how it could be done.