Introduce a new annotation propagationpolicy.karmada.io/generation

[chaunceyjiang]

What type of PR is this?
/kind feature

What this PR does / why we need it:

Previously, a new feature was introduced for PP via #4602. Simply put, when the PP is changed, it will not take effect immediately. It only takes effect when the resource template selected by the PP changes.

However, this has raised a new issue in our product. Users cannot quickly determine whether the current resource template has applied the latest PP.

Therefore, I am introducing a new annotation here that stores the generation of an already effective PP. This way users can quickly confirm whether they have applied the latest PP by comparing if their generation is equal.

Which issue(s) this PR fixes:

When PropagationPolicy is in Lazy mode, introduce a new annotation propagationpolicy.karmada.io/generation and clusterpropagationpolicy.karmada.io/generation.

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Introduce a new annotation propagationpolicy.karmada.io/generation

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[chaunceyjiang]

/cc @chaosi-zju PTAL.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 33 lines in your changes missing coverage. Please review.

Project coverage is 28.22%. Comparing base (f869fba) to head (3e53285).
Report is 18 commits behind head on master.

Files	Patch %	Lines
pkg/detector/detector.go	0.00%	30 Missing ⚠️
pkg/detector/preemption.go	0.00%	3 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5156      +/-   ##
==========================================
+ Coverage   28.21%   28.22%   +0.01%     
==========================================
  Files         632      632              
  Lines       43553    43590      +37     
==========================================
+ Hits        12289    12305      +16     
- Misses      30367    30388      +21     
  Partials      897      897              

Flag	Coverage Δ
unittests	28.22% <0.00%> (+0.01%)	⬆️

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[chaosi-zju]

/assign

Thanks, this is a nice improvement!

I'll take a closer look tomorrow.

[chaosi-zju]

Do you think it is necessary to add generation annotations to ResourceBinding to improve observability?

[chaunceyjiang]

Do you think it is necessary to add generation annotations to ResourceBinding to improve observability?

I'm not sure, we don't have that requirement at the moment.

[chaosi-zju]

It seems fine, but I suggest bringing this generation annotation regardless of whether lazy or not, but not refreshing the generation when resourceChangeByKarmada && util.IsLazyActivationEnabled(policy.Spec.ActivationPreference), because the current code is too complex and difficult to understand.

CC @RainbowMango

[RainbowMango]

However, this has raised a new issue in our product. Users cannot quickly determine whether the current resource template has applied the latest PP.

A question is whether your product uses the Lazy feature? If I remember correctly, you would not make use it at all.

It seems a general requirement that users want to know whether their workload is correctly handled by specific PropagationPolicy, now we have the permanent ID on the resource template, but we still lack more accurate info to figure out if subsequent changes are applied or not.

[chaunceyjiang]

A question is whether your product uses the Lazy feature? If I remember correctly, you would not make use it at all.

Yes, our product has not yet adopted it. The plan is to introduce some features of Karmada into our product this month. We have conducted research on this special effect and after internal discussions, we found the problem I described in the issue.

Before introducing this special effect, we always assumed that PP takes effect immediately, so our product can find the effective PP through the PP name and PP namespace on the resource template.

[RainbowMango]

Yes, our product has not yet adopted it. The plan is to introduce some features of Karmada into our product this month.

If you do mean the Lazy feature, please give it another thought except you have a split use case and verified thoroughly.
Because this feature lacks enough feedback and has some kind of relationship with #5118, particularly when thinking of introducing pause to PP.