[test] statefulset controller: fix requests tracker concurrency

[atiratree]

What type of PR is this?

/kind bug
/kind flake

What this PR does / why we need it:

fixes a flake when using Parallel PodManagementPolicy (burst) in StatefulSets

Which issue(s) this PR fixes:

Fixes #124526

Special notes for your reviewer:

tested with the stress tool

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[atiratree]

/triage accepted
/priority important-longterm

[ingvagabund]

Can you more elaborate on why the current implementation does not work as expected? I.e. what's the underlying cause that makes the test flake? And what has changed and how it removes the flakiness?

[atiratree]

We set excpected failure here after 2 requests:

kubernetes/pkg/controller/statefulset/stateful_set_control_test.go

Line 523 in 0590bb1

om.SetCreateStatefulPodError(apierrors.NewInternalError(errors.New("API server failed")), 2)

Then we scale up the replica set in parallel (Burst).

kubernetes/pkg/controller/statefulset/stateful_set_control_test.go

Line 525 in 0590bb1

if err := scaleUpStatefulSetControl(set, ssc, om, invariants); !isOrHasInternalError(err) {

Then the pod tracker is called.

kubernetes/pkg/controller/statefulset/stateful_set_control_test.go

Line 2516 in 0590bb1

if om.createPodTracker.errorReady() {

Each tracker method is thread safe but they are not thread safe together. This is the reason behind the flake.

So we fix that by locking the increment and error checking with a single lock.

---

Also we have the parallel requests checking which is independent and used in TestParallelScale test.

kubernetes/pkg/controller/statefulset/stateful_set_control_test.go

Line 2946 in 0590bb1

func TestParallelScale(t *testing.T) {

This was guarded by a lock before and maxParallel was always equal to the number of requests. So it didn't test the parallelness correctly and had to be fixed as well.

[ingvagabund]

expectedMinParallelRequests is a new field? Why the original 1 is not enough?

[atiratree]

I have moved this refactoring to a new commit: 7b725f3.

This is to make the test more accurate as originally we expected only 2 parallel requests. But if we create a 1000 pods we should expect more, otherwise it would suggest a regression.

[ingvagabund]

Why is (diff < -1 || diff > 1) no longer tested?

[atiratree]

this was replaced by the expectedMinParallelRequests as the test case above can specify the expected number of requests for a diff they expect

[ingvagabund]

Worth mentioning:

• with trackParallelRequests locking the parallel requests/routines are serialized which makes the testing less real (some of the state space is not explored).
• removing reset of both delay and parallel fields is ok since they execution path does not generate the error so the reset code is actually never executed -> safe to remove the code resetting both fields

[atiratree]

with trackParallelRequests locking the parallel requests/routines are serialized which makes the testing less real (some of the state space is not explored).

I have solved this by requiring the enablement for the tracking

https://github.com/kubernetes/kubernetes/pull/124624/files#diff-49263a54d6a7753728e489881537462578ddc2b9b09404ee335c73e27e178ddcR2436-R2438

so it should not affect the other tests now, apart from the TestParallelScale

---

I have also added a check for the expectedMinParallelRequests values.

https://github.com/kubernetes/kubernetes/pull/124624/files#diff-49263a54d6a7753728e489881537462578ddc2b9b09404ee335c73e27e178ddcR2990-R2994

[ingvagabund]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 9efa79f0eea8c3b1ddaaa63a3763993f5280d538