Ease file permission issues on Linux by injecting UID/GID

[jeffgeorge]

Hi @EvanDarwin, thanks so much for doing the groundwork to get a replacement for Bitnami's docker images.

I had a great time building out a migration plan from Bitnami to your image, and it worked perfectly on MacOS, but when I moved it to my eventual production linux server I hit a bunch of issues with file ownership.

Upon digging further, I found you're manually creating a phpbb user and group (receiving UID=100 and GID=101), which is understandably freaking out on my host if I try to set up any volumes in the /opt/phpbb directory tree.

I don't know the best way to do this, but I have a proof of concept here. It's very ugly, because I have to pass the parameters through build.sh -> Dockerfile because the phpbb user is created in the Dockerfile.

I've seen other Docker containers that expose environment variables for UID/GID as Compose environment variables. I don't particularly care how it's implemented, I'd just love to be able to add like:

    environment:
      - PUID=1001
      - PGID=1001

And end up with those settings, and get the defaults if you don't pass vars. . . but I think that would require a larger refactor, such that the user is created outside of the image build process.

Alternatively, it looks like there's some kind of way to do this without explicitly creating a user, by using the user directive.