fix: honor --stderrthreshold flag when --logtostderr is enabled

[pierluigilenoci]

What this PR does

When --logtostderr is enabled (which is the default in klog and explicitly set in all entry points), klog's legacy behavior silently ignores the --stderrthreshold flag. This means users cannot filter log output by severity level, even though the flag appears to be available.

This PR opts into the fixed behavior introduced in klog v2.140.0 by setting:

• legacy_stderr_threshold_behavior=false — disables the legacy override
• stderrthreshold=INFO — preserves the current default behavior

After this change, users can set --stderrthreshold=WARNING (or any level) and it will work as expected.

All entry points in cmd/ are updated:

• cmd/machineset
• cmd/nodelink-controller
• cmd/vsphere
• cmd/machine-api-operator (start + version subcommands)
• cmd/machine-healthcheck

klog dependency updated from v2.130.1 to v2.140.0 (which introduces the legacy_stderr_threshold_behavior flag).

Why

See upstream fix: kubernetes/klog#432

Testing

• Verified machine-api-operator builds successfully with updated dependency
• Verified --stderrthreshold=WARNING now correctly filters output when --logtostderr is enabled

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Run ID: 7ee90481-1c9e-48ca-89f1-e4cb11d93c66

📥 Commits

Reviewing files that changed from the base of the PR and between 994d225 and b66c2e6.

📒 Files selected for processing (1)

• cmd/machine-healthcheck/main.go

---

Walkthrough

Added programmatic klog flag settings across multiple command entrypoints and bumped klog to v2.140.0: each entrypoint now sets logtostderr=true, disables legacy_stderr_threshold_behavior, and sets stderrthreshold=INFO (with failure handling).

Changes

Cohort / File(s)	Summary
klog Dependency Update go.mod	Bumped k8s.io/klog/v2 from v2.130.1 to v2.140.0.
Stderr threshold & klog flag config cmd/machine-api-operator/start.go, cmd/machine-api-operator/version.go, cmd/machineset/main.go, cmd/nodelink-controller/main.go, cmd/vsphere/main.go, cmd/machine-healthcheck/main.go	After enabling logtostderr=true, added flag.Set calls to set legacy_stderr_threshold_behavior=false and stderrthreshold=INFO; each call is checked and failure triggers klog.Fatalf.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Assessment against linked issues

Objective	Addressed	Explanation
Fix stderrthreshold being ignored when logtostderr=true [#432]	✅
Enable opt-in severity filtering via legacy_stderr_threshold_behavior flag [#432]	❌	Code force-sets legacy_stderr_threshold_behavior=false programmatically, which opts into the new behavior by default instead of leaving legacy behavior as the default opt-in state.
Set stderrthreshold to a specific level for filtering [#432]	✅

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.11.4)

Error: can't load config: unsupported version of the configuration: "" See https://golangci-lint.run/docs/product/migration-guide for migration instructions
The command is terminated due to an error: can't load config: unsupported version of the configuration: "" See https://golangci-lint.run/docs/product/migration-guide for migration instructions

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[openshift-ci]

Hi @pierluigilenoci. Thanks for your PR.

I'm waiting for a openshift 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.

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[pierluigilenoci]

cc @JoelSpeed @damdo — This is a straightforward klog fix to honor the `--stderrthreshold` flag when `--logtostderr` is enabled. Part of a broader campaign to fix this across the Kubernetes ecosystem (see kubernetes/klog#432). Would appreciate a review when you get a chance!

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@cmd/machine-healthcheck/main.go`:
- Around line 81-89: After calling klog.InitFlags(nil) in main (klog.InitFlags),
set the logtostderr flag to "true" like the other entry points do so the stderr
threshold behavior is applied consistently; add a flag.Set("logtostderr",
"true") immediately after klog.InitFlags(nil) alongside the existing flag.Set
calls for "legacy_stderr_threshold_behavior" and "stderrthreshold" to ensure
klog writes logs to stderr as expected.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 7a5fba2b-55e2-4542-9ca5-20c81ca353ad

📥 Commits

Reviewing files that changed from the base of the PR and between b8fd345 and e6831c9.

⛔ Files ignored due to path filters (11)

• go.sum is excluded by !**/*.sum
• vendor/k8s.io/klog/v2/README.md is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/internal/serialize/keyvalues.go is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/internal/serialize/keyvalues_no_slog.go is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/internal/serialize/keyvalues_slog.go is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/klog.go is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/klogr.go is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/klogr_slog.go is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/textlogger/options.go is excluded by !vendor/**, !**/vendor/**
• vendor/k8s.io/klog/v2/textlogger/textlogger.go is excluded by !vendor/**, !**/vendor/**
• vendor/modules.txt is excluded by !vendor/**, !**/vendor/**

📒 Files selected for processing (7)

• cmd/machine-api-operator/start.go
• cmd/machine-api-operator/version.go
• cmd/machine-healthcheck/main.go
• cmd/machineset/main.go
• cmd/nodelink-controller/main.go
• cmd/vsphere/main.go
• go.mod

[JoelSpeed]

/ok-to-test