fix: honor -stderrthreshold when -logtostderr=true

[pierluigilenoci]

What

Opt into the fixed klog behavior so that -stderrthreshold is respected even when -logtostderr=true (the default).

Why

klog v2 defaults -logtostderr to true. When active, the -stderrthreshold flag is silently ignored — all log severities are unconditionally written to stderr. This makes it impossible for log-aggregation systems to filter by severity.

This has been an open issue since 2020: kubernetes/klog#212

The fix was merged in klog v2.140.0 via kubernetes/klog#432 (authored by me) and introduces an opt-in flag legacy_stderr_threshold_behavior. Setting it to false enables the corrected behavior where -stderrthreshold is honored.

What changes

After klog.InitFlags(), two flags are set in all 3 entry points:

• legacy_stderr_threshold_behavior=false — enables the fix
• stderrthreshold=INFO — preserves current behavior (all severities still go to stderr by default)

Since these are set before flag parsing, users can now override -stderrthreshold=WARNING or -stderrthreshold=ERROR on the command line and it will actually work.

Files modified

• cmd/auth-provider-gcp/main.go
• cmd/gke-gcloud-auth-plugin/cred.go
• metis/cmd/main.go

References

• Upstream issue: stderrthreshold not honored when logtostderr is set klog#212
• Upstream fix: feat: fix stderrthreshold not honored when logtostderr is set (#212) + two new flags klog#432

[k8s-ci-robot]

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This pull-request has been approved by: pierluigilenoci
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[k8s-ci-robot]

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[hdp617]

/ok-to-test