Hi @JulienBalestra. Thanks for your PR.

I'm waiting for a containerd member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

So, what tools are creating images with the docker zstd mediatype? I thought the goal would be to work towards an OCI media type for zstd although I know that discussion has somewhat stalled. It would be good to understand the intention going forward since we already support zstd compression, just not using a unique media type at this point.

According to moby/buildkit#3968 and comments in moby/buildkit#2344, buildkit is capable of producing application/vnd.docker.image.rootfs.diff.tar.zstd.

How impactful is this really? It seems years ago BuildKit had an experimental support for zstd with this non-standard media type and then it full added support with the standard OCI media type. Our recommendation here would normally be to re-build anything that was built with an experimental version. Its a small change but the impact still needs to be evaluated. We usually only accept these types of changes with a comment explaining why it is there and the range of impact (which version of the builder and when it was deprecated/removed).

then it full added support with the standard OCI media type

You're reading moby/buildkit#3968 the wrong way. It added an ability to unpack application/vnd.docker.image.rootfs.diff.tar.zstd. I believe that current buildkit code as of 0.13.x is still able to both produce and consume it.

Thank you all for your feedback !

So, what tools are creating images with the docker zstd mediatype?

As @slonopotamus mentioned, it's possible to use zstd compression with buildx like:

docker buildx build ... \
--output compression=zstd,force-compression=true,push=true,type=image,compression-level=22

Officially documented here.

@estesp & @dmcgowan you would be more inclined to migrate to OCI media for use cases that require a different compression than gzip ?

Latest versions of buildkit create OCI mediatypes by default but users can set oci-mediatypes=false as output option. If they request both zstd and --oci-mediatypes=false, then the mediatype is application/vnd.docker.image.rootfs.diff.tar.zstd.

@JulienBalestra I would say it is our expectation that newer functionality is using the OCI media types, but ultimately the application/vnd.docker. namespace is determined by docker/moby tools. If these are still being produced and supported by the build tools, then we can add it. I didn't want to add support for something that was already deprecated. Thanks for the context @tonistiigi

Shouldn't this be +zstd not .zstd?

@jonjohnsonjr For the OCI mediatypes, I would expect +zstd. It looks like Buildkit is producing a Docker mediatype with .zstd matching the existing .gzip.

That is really unfortunate.

This fixed #9263