Push zstd::chunked compressed container images to another tag

[travier]

Using a better compression algorithm will mean smaller container images in the registry and faster pulls.

As the spec does not support multiple compression algorithms for a single tag, we should push those images to another tag.

See:

• https://www.redhat.com/sysadmin/faster-container-image-pulls
• What are your plans about zstd:chunked containers/podman#15126
• How to generate a zstd:chunked image ? containers/podman#15113
• --compression-format= for podman: https://docs.podman.io/en/latest/markdown/podman-push.1.html
• --dest-compress option for skopeo: https://github.com/containers/skopeo/blob/main/docs/skopeo-copy.1.md
• Enable zstd:chunked support in containers/image containers/storage#775
• pkg/compression: new zstd variant zstd:chunked containers/image#1084
• support zstd as archive format moby/moby#28394 (comment)
• Formalize support for zstd compression: v1.1.0 ? opencontainers/image-spec#803 (comment)

[travier]

According to https://fedoraproject.org/wiki/Changes/zstd:chunked, container engine mostly support this format now.

But that would require some testing to not break older systems. So the push 2 times route is probably the safest in the short term. It should be reasonably easy to do.

[travier]

Apparently it's possible to push both formats using a manifest list: https://discussion.fedoraproject.org/t/switch-fedora-container-images-to-support-zstd-chunked-format-by-default/123712/8

I will give this a try.

[sanmai-NL]

@travier Good work! What's your current status?

[travier]

It's stuck on #129 (review). We need to either implement this support in https://github.com/redhat-actions/push-to-registry or switch to using https://github.com/ublue-os/push-to-registry/tree/scaffold-repository in the meanwhile. I would prefer the first option, even if it's from a fork and not merged for now.