Personal Base Container

This is my personal base container for Docker. It provides a basic Ubuntu 20.04 (aka "Focal") or 22.04 (aka "Jammy") image. Maybe you'll find it helpful too...

How to Use This

The container will probably not be used directly, but rather as a for building other (Docker) containers on. To do that, specify this as your base image (in your Dockerfile):

FROM ghcr.io/minchinweb/base:jammy

# ... and the rest

You also probably want to set the UID and GID (User ID number and Group ID number). This can be done through the environmental variables PUID and GUID (either the -e option at the command line, or the environment key in your docker-compose.yaml file).

There is also a folders at /app, /config, /defaults that are owned by the user. The idea is to have your application use this /config volume for all its persist-able data, and do this by mounting this as a volume outside of your container (either the -v option at the command line, or the volumes key in your docker-compose.yaml file).

Why I Created This

or, What Problems is This Trying to Solve?

Docker works it's magic by isolating processes, rather than spinning up a whole new virtual machine. This is great for hardware requirements (especially as you add more and more containers), but one of the byproducts is that certain aspects of the processes run within the containers filter out into the host operating system, in particular the user (and group) that a process is run by inside the container is the same user (and group) that is running the process outside the container, on the host system. Further more, this user is not identified by a name, but rather a number. The naïve approach is just to run everything as root (user id 1) because the user id is constant across systems; however it's strength (that root has access to (pretty much) everything) is also a great weakness (that it can stomp all over your system, including changing or deleting pretty much any file on your system). Running your containers as root also is the antithesis to much of Linux security model, which requires processes to run as users with only the permissions they need, and no extras. Thus, a better model is to create docker user on your host system (name it whatever you want) that can only edit the docker volumes on your host system, and map that user id (and group id) to the user running the process within your container, and give that user (within the container) whatever permissions it may need. Within the container, this user is named abc and belongs to the abc group.

As another bonus, Docker will cache layers (the parts a container is built up of), and so by using a constant base image on in my Docker setup, it saves on space.

Personal Additions and Notes

• add various tags as per label-schema.org
• added Canadian English locale, and sets the language to this
• init script is found at /s6-init. Turns out naming the process init causes weird Docker bugs
• when built on Docker Hub via GitHub Actions and published to the GitHub Container Registry, is tagged with "latest", the Ubuntu codename (e.g. "focal"), and the Git commit ID (a randomish string of numbers and letters)

Prior Art

This is based on LinuxServer.io's base container. This is where I first became aware of the user id problem and this solution, and also the idea of a constant /config volume for all containers. However, LinuxServer.io only has a certain selection of containers that they maintain, and I wanted to apply this set up to other containers. By the time I'd figured out how the system working, I'd basically rebuilt their base container.

• what LinuxServer.io says about PUID and GUID
• what LinuxServer.io says about container volumes

Alpine Linux is often used as a base for container, owing to its small size (quoted at ~5MB). However, I figure the trade off of being able to use Ubuntu under the hood, and not being required to learn yet another variant of Linux, is worth slightly larger size (this image comes in at ~44MB).

s6-overlay is a project used by LinuxServer.io, and so used here too, to deal with containers that launch multiple processes. The s6 system is used to run the scripts that fix the user id problem.

Known Issues

• For whatever reason, I couldn't get this image to build locally and work. However, it works when built on Docker Cloud/Docker Hub.
• /init still exists, but don't use it. Use /s6-init instead (see here)
• I've had some issues getting services under the init system to work. I haven't gotten it solved yet, so I'm not sure whether the issue is something with it, or something with my code...
• this image doesn't automatically rebuild when the upstream image changes, but I have set up GitHub Actions to rebuild this image every week to approximate that automation.
• if you use this as a base image, you may need to set ENV S6_KEEP_ENV=1 in your Dockerfile if you want your default script to have access to your environmental variables.