Docker image strategy is not compatible with multiple users sharing Docker resources

[rmartin16]

Describe the bug

A use-case for Briefcase requires the creation of Docker images that are unique to the user that created the image; that is, the UID of the brutus user inside the image is the same as the user that ran Briefcase.

However, if different users on the same machine run the same Briefcase command, e.g. briefcase build linux system --target debian:bookworm, each user will create a docker image tagged as briefcase/com.example.helloworld:debian-bookworm....but the images will be different for each user.

When multiple users run such a briefcase command, each subsequent user will clobber the image created by the previous user. If users run such a briefcase command concurrently, they are likely to use an image created for another user and the command will likely fail.

Steps to reproduce

Run briefcase build linux system --target debian:bookworm as two different users on the same machine where Docker resources are being shared. AFAICT, Docker images will be shared in a typical installation; although, I'm less sure of how Docker would be configured on a machine that is expected to be shared by multiple users concurrently...

Expected behavior

The Docker image tags are not clobbered by other users.

Screenshots

No response

Environment

• Operating System: ubuntu 23.10
• Python version: 3.11
• Software versions:
  • Briefcase: 0.3.17.dev205+ga995b09f

Logs

No response

Additional context

No response

[freakboy3742]

Ugh. This is messy.

A couple of possible avenues to explore for a fix:

1. Include the user name in the docker tag (or, use a some sort of per-user namespace in the tag name)
2. Modify the Dockerfile so that the username/userID isn't hard-coded in the Docker file, but is provided as an environment variable. I'm not 100% sure this will be feasible, as manipulating the UID is a key part of the Dockerfile working.
3. Work out how to configure Docker to have a per-user image cache. I don't even know if this is possible.

[rmartin16]

2. Modify the Dockerfile so that the username/userID isn't hard-coded in the Docker file, but is provided as an environment variable. I'm not 100% sure this will be feasible, as manipulating the UID is a key part of the Dockerfile working.

Creating the user could theoretically be moved in to an entrypoint script for the image. In that way, the user would be created each time a container is spun up. I would need investigate the exact semantics of making this step transparent...but I presume it would then just be executing the remaining docker arguments within the container after becoming the new user...