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[kolla][tripleo] Podman/buildah


Hi,

At the Denver forum during the kolla feedback session [1], the topic
of support for podman [2] and buildah [3] was raised. RHEL/CentOS 8
removes support for Docker [4], although presumably it will still be
possible to pull down an RPM from https://download.docker.com/linux/.

Currently both kolla and kolla-ansible interact with docker via the
docker python module [5], which interacts with the docker daemon API.
Given that podman and buildah are not daemons, I would expect the
usage model to be a bit different. There is a python API for podman
[6] which we might be able to use.

I understand that Tripleo uses buildah to build images already (please
correct me if I'm wrong). How is this achieved with kolla? Perhaps
using 'kolla-build --template-only' to generate Dockerfiles then
invoking buildah separately? Are you planning to work on adding
buildah support to kolla itself?

For running services, Tripleo uses Paunch [7] to abstract away the
container engine, and it appears Podman support was added here -
building CLI argument strings rather than via a python API [8].

For anyone using kolla/kolla-ansible, please provide feedback on how
useful/necessary this would be to you.

Thanks,
Mark

[1] https://etherpad.openstack.org/p/DEN-train-kolla-feedback
[2] https://podman.io/
[3] https://buildah.io/
[4] https://access.redhat.com/solutions/3696691
[5] https://github.com/docker/docker-py
[6] https://github.com/containers/python-podman
[7] https://docs.openstack.org/developer/paunch/readme.html
[8] https://github.com/openstack/paunch/blob/ecc2047b2ec5eaf39cce119abe1678ac19139d79/paunch/builder/podman.py