Fix TGB webhook error message to report changes to immutable field

[maruina]

Issue

Description

Flux is not able to delete and re-create a TargetGroupBinding object when users try to change an immutable field. The issues has been reported in fluxcd/kustomize-controller#834

This is because the kustomize-controller is using those regular expressions to detect immutable errors returned by custom admission webhooks and Kubernetes CEL.

This PR is changing the error message to match the regular expression

regexp.MustCompile(`.*immutable\sfield.*`)

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

Welcome @maruina!

It looks like this is your first PR to kubernetes-sigs/aws-load-balancer-controller 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes-sigs/aws-load-balancer-controller has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[k8s-ci-robot]

Hi @maruina. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

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.

[zac-nixon]

/lgtm
/ok-to-test

[maruina]

Tested manually in a cluster. After updating the AWS load balancer controller with this PR, the kustomize-controller is detecting an immutable field, deleting the TGB and re-creating it

kubectl -n flux-system describe kustomizations.kustomize.toolkit.fluxcd.io XYZ
[...]
Events:
  Type     Reason                Age                   From                  Message
  ----     ------                ----                  ----                  -------
  Warning  ReconciliationFailed  6m49s (x131 over 2d)  kustomize-controller  TargetGroupBinding/XYZ dry-run failed (Forbidden): admission webhook "vtargetgroupbinding.elbv2.k8s.aws" denied the request: TargetGroupBinding update may not change these fields: spec.targetGroupARN
  Warning  ReconciliationFailed  52s                   kustomize-controller  TargetGroupBinding/XYZ immutable field detected, failed to wait for object to be deleted: context canceled
  Normal   Progressing           18s                   kustomize-controller  TargetGroupBinding/XYZ created
  Normal  Progressing              18s  kustomize-controller  Health check passed in 77.803065ms
  Normal  ReconciliationSucceeded  18s  kustomize-controller  Reconciliation finished in 1.188936124s, next run in 10m0s

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

Approval requirements bypassed by manually added approval.

This pull-request has been approved by: maruina

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[zac-nixon]

Thanks for the PR.