arm64 Mariner core 1.0 and 2.0 missing Variant in `docker inspect` results

[dagood]

My build depends on the Mariner image Variant for arm64 in a few ways, so this caused a build error for me.

It looks like Variant shows up in the manifest, but not in the image metadata:

$ docker pull --platform linux/arm64/v8 mcr.microsoft.com/cbl-mariner/base/core:1.0
..
Status: Downloaded newer image for mcr.microsoft.com/cbl-mariner/base/core:1.0
mcr.microsoft.com/cbl-mariner/base/core:1.0

$ docker manifest inspect mcr.microsoft.com/cbl-mariner/base/core:1.0
...
         "platform": {
            "architecture": "arm64",
            "os": "linux",
            "os.version": "cbl-mariner-1.0",
            "variant": "v8"
         }
...

$ docker inspect -f "{{ .Architecture }}/{{ .Variant }}" mcr.microsoft.com/cbl-mariner/base/core:1.0
arm64/

The final result should be arm64/v8. Based on build logs from Feb 15 at 9:22 AM, this is a regression:

-- EXECUTING: docker inspect -f "{{ .Architecture }}/{{ .Variant }}" cblmariner.azurecr.io/base/core:1.0
arm64/v8

(The above commands have the same results with cblmariner.azurecr.io/base/core:1.0 and mcr.microsoft.com/cbl-mariner/base/core:1.0 as far as I can tell.)

I'm going to try changing my build to stop checking that the arch/variant is correct because we've been broken by this during both of our most recent two releases. But I still figured I should report/ask about it.

• Related, an earlier issue where the manifests suddenly changed to include the variant: core:1.0 Docker image now includes v8 variant in arm64 manifest #4856

/cc @microsoft/golang-compiler @mthalman

[mfrw]

/cc @mandeepsplaha