Specify the arch passed as build arg in the distroless image (#848)

[Serializator]

What this PR does / why we need it:
I moved ARG ARCH to the start so that it can be used in the last stage (gcr.io/distroless/static:latest-$ARCH). It is declared again below FROM golang:1.17.1 as build so that it is available when make metrics-server is run.

I tested with the architectures defined in the Makefile, each of which worked as expected.
https://github.com/kubernetes-sigs/metrics-server/blob/master/Makefile#L14

$ docker buildx build -t kubernetes-sigs/metrics-server:<arch> \
    --build-arg ARCH=<arch> \
    --build-arg GIT_COMMIT=foo \
    --build-arg GIT_TAG=bar .

"foo" and "bar" came back in the logs for make metrics-server as well, indicating that these are available as environment variables. I wanted to test this as well because I only noticed later that ARCH was not available anymore when I moved ARG ARCH to the start.

I don't know exactly where these images are built but it would be better to compare the architecture of the image that was built with the expected architecture, to prevent a regression in the future.

Which issue(s) this PR fixes:
Fixes #848

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[serathius]

I have verified locally that this fix works, great job!
Aside one nit, this looks good to be merged.

As for testing we should be able to confirm by checking image pushed after merge gcr.io/k8s-staging-metrics-server/metrics-server:master

[Serializator]

Thank you! I made the necessary changes according to your feedback.

[serathius]

/ok-to-test

[serathius]

Ups, looks like you need to specify default for

metrics-server/skaffold.yaml

Line 13 in 85a18b5

buildArgs:

[Serializator]

Ups, looks like you need to specify default for

metrics-server/skaffold.yaml

Line 13 in 85a18b5

buildArgs:

I added "amd64" as the default 👍🏼

[serathius]

/retest

[Serializator]

As for testing we should be able to confirm by checking image pushed after merge gcr.io/k8s-staging-metrics-server/metrics-server:master

@serathius What about adding it as a structure test in the Skaffold configuration? I looked through the kind of structure tests there are but none of them seem related to the metadata of the image, most of them seem to be ran from within the container.

[serathius]

As for testing we should be able to confirm by checking image pushed after merge gcr.io/k8s-staging-metrics-server/metrics-server:master

@serathius What about adding it as a structure test in the Skaffold configuration? I looked through the kind of structure tests there are but none of them seem related to the metadata of the image, most of them seem to be ran from within the container.

Sure, maybe instead of adding it to Skaffold tests that run k8s cluster, we might want to expand cli tests https://github.com/kubernetes-sigs/metrics-server/blob/master/Makefile#L128-L133 as they just use docker to check image.

[serathius]

This should be good to merge. We can add tests as separate PR.

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: serathius, Serializator

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[serathius]

Confirmed that problem was fixed

~ $ docker pull --platform linux/ppc64le gcr.io/k8s-staging-metrics-server/metrics-server:master
master: Pulling from k8s-staging-metrics-server/metrics-server
e5decac5defe: Pull complete 
1f48636f6f92: Pull complete 
Digest: sha256:b3b6ca00d7bd8211f2e74115ad121be6d2ae8eda9a187ef4e0c60e83ed6be0d8
Status: Downloaded newer image for gcr.io/k8s-staging-metrics-server/metrics-server:master
gcr.io/k8s-staging-metrics-server/metrics-server:master
~ $ docker inspect gcr.io/k8s-staging-metrics-server/metrics-server:master | grep Arch
        "Architecture": "ppc64le",