Podman support

[gastaldi]

It would be really nice if TestContainers supported podman.
This is a real game changer to no longer depend on Docker daemons to run.

[bsideup]

Thanks for asking! Since this is not the first time somebody asks for Podman, I would like to post a (non complete, most probably) list of requirements we need to do the Testcontainers' magic:

• Cross-platform support. It should work exactly the same on Linux, Mac and Windows, without having us do the VM management
• Docker networks, ability to start/connect/disconnect containers with/to Networks
• Image management - pulling (including the various authorisation mechanisms), listing, building
• Long running processes that survive the test run
• Access to /var/run/docker.sock from inside the container, ability to do regular Docker commands with it
• Log access/streaming
• Stdin/Stdout/Stderr streaming
• There are many Docker images that require root user, these should work too
• Volumes management

I am not a Podman expert, and if somebody from the community can help clarifying these, I would be happy to learn, and, as long as every point is clarified (the list is not 100% complete and we may need to add more in future) we can consider adding the support for Podman.

[bsideup]

and BTW, "daemonless" here makes it harder for Testcontainers :)

[gastaldi]

From my Podman experience:

• Access to /var/run/docker.sock : I don't think so, since there is no daemon;
• Cross Platform support: Podman only works in Linux. I haven't checked the internals of Testcontainers yet, but Podman offers an alias to replace the docker command, so Testcontainers could use Podman in Linux with the same CLI syntax as used in Docker (if the CLI is used);
• Image Building: is performed by Buildah

I wish @rhatdan could chime in the discussion to clarify or correct my statements 😃

[bsideup]

if the CLI is used

We're not using the CLI, but the REST API.

It looks to me that we should rather focus on waiting for the rootless Docker (an ongoing effort upstream), Podman as it is (plus Buildah, plus whatever else is needed) cannot provide the same functionality we need to do what we're doing in Testcontainers.

[Kidlike]

Dropping this here because I found it useful and relevant to the discussion :)

https://medium.com/nttlabs/cgroup-v2-596d035be4d7

[ppalaga]

We're not using the CLI, but the REST API.

Podman recently started offering a REST API: https://podman.io/blogs/2020/01/17/podman-new-api.html

[bsideup]

@ppalaga nice!

Do you have a compatibility table or something, to see which Docker's API endpoints are supported or not? Thanks!

[crunchtime-ali]

@bsideup
I would help putting that table together. Is there a list of Docker API endpoints (and options) testcontainers uses or a test-suite we can run against podman's Docker compability API.

[bsideup]

@crunchtime-ali I believe running Testcontainers' test suite is the best way to check whether all APIs are supported or not. Our tests should cover all types of Docker features we are using.

You can also start a TCP proxy between Testcontainers and Podman to collect the list of endpoints that are used.

[rocketraman]

Some more information that might be helpful:

https://github.com/containers/libpod/blob/master/docs/source/markdown/podman-system-service.1.md

https://github.com/containers/libpod/blob/master/API.md

The Podman API supposedly has a docker API compatible endpoint.

[rocketraman]

And it can also expose a sock socket file as well, which should meet the requirement of having a /var/run/docker.sock (or equivalent) inside the container.

[rhatdan]

Correct we are under heavy development and are looking at testcontainers to prove that we handle the Docker API correctly. We have an extended version to support advanced features of Podman as well.

[cevich]

I'm also looking at doing the reverse: Running testcontainers tests in podman CI. Solving the challenges here, will help me get to there. (subscribed)

[baude]

how does one run the test suite? hints around how to specify the sock to connect to is a bonus. ill do the work.