Add Docker Container

[ccremer]

Hello! Thanks for this awesome ZFS management tool! I would like to run znapzend packaged in a (docker) container support

What this PR does

It adds

• a Dockerfile which builds an Alpine-based container image with znapzend and ZFS in it.
• Documentation on the its usage
• changes to include Docker builds in the CI pipeline. The pipeline assumes now following workflow
  • Every branch builds the Perl software, runs unit test and builds the container image
  • Only the master branch pushes the built container image to Docker hub with "master" tag
  • When tagging a commit with a new version release, this tag is pushed to Docker hub.
• removed old Perl versions in the Pipeline. In my fork, they were failing in Travis, and I'm not fluent in Perl at all to fix the errors I encountered.

The master container tag on Docker Hub is similar to latest, but I often find latest ambiguous, as it's never clear whether "latest" means "latest (dev) build" or "latest stable", or whatever. With master it's clear that it corresponds to the master branch.

Please let me know if there are more dependencies (other than ZFS, mbuffer) needed in the container runtime image.

Why this PR is needed

• Easier distribution and run of znapzend. Just docker run ... and the tool is installed in seconds.
• Easier versioning and rollbacks or uninstallations.
• There are a few Docker images of znapzend already available, but they are often outdated (including mine, but it's for testing this pipeline change). With the integration into this repository, Docker builds become part of the development and thus maintained.

Currently, the container needs to run privileged. I haven't invested the time to investigate why or if it can run unprivileged. The configuration store in ZFS properties comes handy, it removes the need to mount a config file.

What else needs to be done

• Create and configure a Docker Hub repository "oetiker/znapzend". You already seem to have a docker Hub user, but not the repository.
• Store the Docker Hub credentials in Travis environment variables in the settings, otherwise Docker push will fail.

[coveralls]

Coverage remained the same at 91.649% when pulling 338527cd4d356c4cac4f1bedf84b7a3247d9be6c on ccremer:container into 62b10796af1535eca2430abc7ec8115e8c6b7141 on oetiker:master.

[ccremer]

how about pushing the docker image to the new github package repo and switching to using github actions for building the whole thing while at it ?

Switching to Github Actions is also my preferred solution, it's faster, better documented and more consistent. I wasn't sure how attached you were to Travis.

I have tried Github package repo once, I recall some limitation but I need to check what that was... let me try again.

running the automated tests with the docker image would be a good thing to veryfy that it is working ...

We could introduce another build stage after the runtime stage (FROM builder as test) and run the unit tests in the buster image. For master branch and tagged releases we can then only build the runtime image with the docker build -t ... --target runtime command.

[ccremer]

Now I know the limitation:

$ docker pull docker.pkg.github.com/ccremer/znapzend/znapzend:master
Error response from daemon: Get https://docker.pkg.github.com/v2/ccremer/znapzend/znapzend/manifests/master: no basic auth credentials

It's not publicly available without a login :( Also, apparently the downloads costs: https://github.com/settings/billing. So I still recommend Docker Hub.

I have now migrated to GitHub actions and also included the tests in the Docker build. Re-added the matrix build with the different Perl versions, but I know that 5.16 definitely fails, so I left that out.

I'm also not sure anymore if Coveralls becomes broken, I had to create a .coveralls.yml in the CI job. Now it passes with a warning, but hopefully that's just because I haven't set up coveralls for this forked repo.

[oetiker]

cool!

[oetiker]

guess I'll have to merge to see if it wall works :) give me a few days