Multi-arch support?

[erikschul]

Would it be possible to uuse umoci for multi-arch images?

I can use skopeo to download a specific arch/os, for both arm64 and amd64, unpack both, modify both, repack both... but then I can't merge them back.

Would it make sense to for umoci to have:

• a merge command that combines tags
• --arch --os filters for unpack from a multiarch manifest, and repack when building a new manifest.

[cyphar]

Yeah this is something I've wanted to figure out a nice way of supporting for a while (as well as providing more generic modification capabilities for descriptors), but I couldn't figure out a nice UX for it.

[erikschul]

@cyphar Do you mean the design of the CLI commands? Perhaps you could write your ideas and people can suggest improvements.

You could also list use cases.

For me, it's:

• download multi-arch image with skopeo (so compatibility, and an e2e test would be nice, especially supporting older versions since debian stable is behind -- https://repology.org/project/skopeo/packages )
• extract from specific OS/arch
• repack into specific OS/arch for a tag (either updating, or creating a new manifest)
• some base images have many arch/os, so if you're only repacking for some arch/os, the others should be removed (i.e. by creating a new manifest rather than updating)
• skopeo may be used to download a specific arch/os, so repack should allow extracting from different base images and repacking into a single image.