Enhance GitHub Actions workflow for multi-platform builds.

[ashokpariya0]

These changes enable building and pushing Docker images for multiple platforms (amd64, arm64, s390x).

What this PR does / why we need it:

As of now, only x86 support is available for the prom-metrics-linter image: https://quay.io/repository/kubevirt/prom-metrics-linter?tab=tags&tag=latest.

This PR introduces changes to enable multi-architecture builds for arm64 and s390x, in addition to x86, using GitHub Actions.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes # #285

Special notes for your reviewer:

Checklist

This checklist is not enforcing, but it's a reminder of items that could be relevant to every PR.
Approvers are expected to review this list.

• Design: A design document was considered and is present (link) or not required
• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Testing: New code requires new unit tests. New features and bug fixes require at least on e2e test
• Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature / API change.
• Community: Announcement to kubevirt-dev was considered

Release note:

None

[ashokpariya0]

Hi @machadovilaca @sradco Could you please review this PR whenever possible??

[sradco]

@avlitman @nunnatsa please review this pr.

[nunnatsa]

This is not needed, for two reasons: the env vars are for the final image, and this is the builder, and also, these ARGs are always set by the CRI.

[ashokpariya0]

I added this for standard single-platform builds (in case we want to build without Buildx) so that we can use the same Dockerfile for both multi-platform builds with Docker Buildx and standard single-platform builds.

[nunnatsa]

It will work without the ENVs in local build. docker/podman will set the TARGEARCH, TARGETOS and TARGETPLATFORMbuild ARGs to the right values. e.g. if you don't mention the --platform - it will be the value of the local platform, and if you do specify the platform, podman/docker will use it to populate these args.

But even without it, the ENVs are only used for the final image, for a running container. ARGs are like build-time env vars. There is no point to set the ENV

[ashokpariya0]

Okay thanks, removed that.
Change

[nunnatsa]

I don't think we need the default value for the TARGETOS, assuming it's always set.

[ashokpariya0]

Okay, Removed.

[nunnatsa]

nit: Thinking about it again, we can do even better. in line 10, we use the TARGETOS parameter, while in line 12 we're using hard coded value of "linux". WDYT about do the same in both case?

either

CGO_ENABLED=0 GOOS=linux GOARCH=${TARGETARCH} go build -v -trimpath -ldflags "-s -w" -o /bin/ .

FROM --platform=linux/${TARGETARCH} gcr.io/distroless/base:latest

or

CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -v -trimpath -ldflags "-s -w" -o /bin/ .

FROM --platform=${TARGETPLATFORM} gcr.io/distroless/base:latest

(TARGETPLATFORM = ${TARGETOS}/${TARGETARCH})

[nunnatsa]

If you want to do it, let's do it in a follow PR.

/lgtm

[ashokpariya0]

Good point, I had considered this earlier. Since cross-compilation for platforms like s390x is only available for Linux, I kept it as linux in the configuration.

The current BUILD_PLATFORMS is set to:

linux/amd64,linux/arm64,linux/s390x

That being said, I’ve opened a PR for symmetry: PR #289.

[nunnatsa]

/lgtm
/approve