feat: Add target-group-prefix annotation to change target group names

[frankh]

Issue

#2553

Description

Currently all target groups start with a prefix of k8s-<namespace>-<name> This is not particularly useful, allow us to override per ingress and service

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 🌟

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[AndrewCharlesHay]

I think it would make sense to imply the trailing dash. So instead of my-service- it would just be my-service and the dash would be added in the concatenation statement

[oliviassss]

/ok-to-test

[frankh]

/retest

[AndrewCharlesHay]

/approve

[AndrewCharlesHay]

@frankh I'm not an official maintainer or anything that was just a suggestion but thanks 😄

[AndrewCharlesHay]

/lgtm

[AndrewCharlesHay]

/retest

[oliviassss]

Thanks for the contribution
/lgtm
assign @M00nF1sh

[AndrewCharlesHay]

@M00nF1sh can we get some 👀 please 🙏

[oliviassss]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AndrewCharlesHay, frankh, oliviassss

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[M00nF1sh]

@frankh @AndrewCharlesHay
sorry for the late review. The change itself lgtm.
However, i'm wondering do we really need to provide this override per Service for your use case? wondering whether it's better to provide this as a controller-level flag instead of annotation on Ingresses.
Personally i prefer to minimize the annotations we expose if possible.

e.g. this could implemented as a controller flag like --tg-name-pattern="k8s-{serviceNamespace:.8s}-{serviceName:.8s}-{hash:10s}"

• Pros:
  1. seems more flexible for all kinds of pattern you want.
  2. avoid need to specify the annotation on every service
  3. less intrusive to Kubernetes service resources. (no need to modify the Service resource's annotation)
• Cons:
  1. unable to provide override per service. (But do we really need this? i doubt it)

note, i used python's format string syntax here, not sure whether there is Golang alternative. However, we can have a naive implementation for pattern like this such as below:

1. use regex to replace {<id>:.<number>s} to be %.<number>s, so it becames k8s-%.8s-%.8s-%.10s
2. then for each extracted <id>, find the value from a variable mapping(serviceNamespace, serviceName, hash), and render it via golang's string.format as additional args.

What do you think?

[AndrewCharlesHay]

@frankh Did you want to take on those changes? I can if you don't want to

[frederiksf]

When can we expect this feature will be released?

[oliviassss]

/retest

[k8s-ci-robot]

New changes are detected. LGTM label has been removed.