Tags immutability should be enforced by PR tests

[danielvegamyhre]

I recently submitted a PR updating the image digest for a tag: #5220

However, I noticed the image digest for registry.k8s.io/jobset/jobset:v0.1.1 never updated, and after discussion with @BenTheElder I learned tags are immutable.

I think this should be enforced on PRs via tests, rather than silently failing in the image promotion process, in order to avoid confusion.

/kind bug

[BenTheElder]

cc @kubernetes/release-engineering

/sig release

[BenTheElder]

This also means that we have manifests that don't match reality and will never be fixed (!)

We should probably revert any tag mutations once we prevent introducing new ones.

I think the only robust way to do this is to parse the full config before and after the PR commits and diff the config in memory, git diff can be misleading so just grepping the diff will cause false positives when config is modified in otherwise acceptable ways (e.g. inserting a new image into a file).

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/lifecycle stale

[xmudrii]

/remove-lifecycle stale

[BenTheElder]

/lifecycle frozen

[BenTheElder]

/help
Ideally we'd have a parser for these configs implemented (see also https://github.com/kubernetes-sigs/promo-tools) and validate that the before/after state of a PR does not involve mutating a tag.

You can use git variables from https://docs.prow.k8s.io/docs/jobs/#job-environment-variables

[k8s-ci-robot]

@BenTheElder:
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In response to this:

/help
Ideally we'd have a parser for these configs implemented (see also https://github.com/kubernetes-sigs/promo-tools) and validate that the before/after state of a PR does not involve mutating a tag.

You can use git variables from https://docs.prow.k8s.io/docs/jobs/#job-environment-variables

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.