fix: honor -stderrthreshold when -logtostderr is set by pierluigilenoci · Pull Request #2421 · openkruise/kruise

pierluigilenoci · 2026-04-23T15:41:46Z

What this PR does

klog v2 defaults -logtostderr to true, which silently causes -stderrthreshold to be ignored — all log messages of every severity are unconditionally written to stderr. There is no way for users to filter which severity levels reach stderr.

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

klog v2.140.0 (kubernetes/klog#432) introduces a legacy_stderr_threshold_behavior flag that fixes this. This PR:

bumps k8s.io/klog/v2 from v2.130.1 to v2.140.0
sets legacy_stderr_threshold_behavior=false after klog.InitFlags in both main.go and cmd/daemon/main.go
sets stderrthreshold=INFO so the default behavior is preserved but users can now override it on the command line (e.g. -stderrthreshold=WARNING)

Why it matters

In production clusters, log aggregation systems (Fluentd, Fluent Bit, Loki, Datadog, etc.) typically ingest logs from container stderr. When every log level goes to stderr indiscriminately:

Log storage costs increase — INFO-level debug noise is stored alongside real errors
Alerting becomes unreliable — operators cannot trigger alerts on stderr output because it contains everything
Signal-to-noise ratio degrades — finding actual errors in a stream of INFO messages is difficult

The -stderrthreshold flag exists precisely to solve this, but it has never worked under the default klog v2 configuration — until now.

Changed files

File	Change
`main.go`	set `legacy_stderr_threshold_behavior=false` + `stderrthreshold=INFO` after `klog.InitFlags`
`cmd/daemon/main.go`	same
`go.mod` / `go.sum`	bump klog v2.130.1 → v2.140.0

klog v2 defaults -logtostderr to true, which silently causes -stderrthreshold to be ignored. klog v2.140.0 introduced the legacy_stderr_threshold_behavior flag that restores the correct interaction between the two flags (see kubernetes/klog#432). This commit: - bumps k8s.io/klog/v2 from v2.130.1 to v2.140.0 - sets legacy_stderr_threshold_behavior=false after klog.InitFlags in both main.go and cmd/daemon/main.go - sets stderrthreshold=INFO so the default behavior is preserved but users can now override it on the command line Ref: kubernetes/klog#212 Signed-off-by: Pierluigi Lenoci <pierluigi.lenoci@gmail.com> Signed-off-by: Pierluigi Lenoci <pierluigilenoci@gmail.com>

kruise-bot · 2026-04-23T15:41:51Z

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kruise-bot · 2026-04-23T15:42:03Z

Welcome @pierluigilenoci! It looks like this is your first PR to openkruise/kruise 🎉

codecov · 2026-04-23T15:55:43Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.85%. Comparing base (d9b8202) to head (ca2d6f5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2421      +/-   ##
==========================================
+ Coverage   48.15%   48.85%   +0.70%     
==========================================
  Files         325      325              
  Lines       34824    27950    -6874     
==========================================
- Hits        16769    13656    -3113     
+ Misses      16523    12763    -3760     
+ Partials     1532     1531       -1

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unittests	`48.85% <ø> (+0.70%)`	⬆️

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Copilot

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates klog to a version that supports honoring -stderrthreshold even when -logtostderr=true, and configures the binaries to use the new behavior while preserving current defaults.

Changes:

Bump k8s.io/klog/v2 from v2.130.1 to v2.140.0.
Set legacy_stderr_threshold_behavior=false and default stderrthreshold=INFO after klog.InitFlags in both entrypoints.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

File	Description
main.go	Opt into new klog stderr-threshold behavior and set default threshold to INFO
cmd/daemon/main.go	Same klog flag defaults as the main binary
go.mod	Bump klog dependency to v2.140.0
go.sum	Update checksums for klog v2.140.0

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Copilot · 2026-04-23T15:56:40Z

+	flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck
+	flag.Set("stderrthreshold", "INFO")                   //nolint:errcheck


flag.Set(...) can fail (e.g., if the flag name changes, isn’t registered due to init order changes, or klog behavior differs between builds). Silencing these errors risks silently reverting to the problematic behavior in production. Consider handling the returned errors and failing fast (or at least emitting a clear warning) so misconfiguration is immediately visible.

Suggested change

flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck

flag.Set("stderrthreshold", "INFO") //nolint:errcheck

if err := flag.Set("legacy_stderr_threshold_behavior", "false"); err != nil {

klog.Fatalf("failed to set flag %q: %v", "legacy_stderr_threshold_behavior", err)

}

if err := flag.Set("stderrthreshold", "INFO"); err != nil {

klog.Fatalf("failed to set flag %q: %v", "stderrthreshold", err)

}

Thanks — good catch. Updated both flag.Set calls in main.go to check the returned error and klog.Fatalf on failure, so misconfiguration is immediately visible instead of silently reverting to the old behavior.

Copilot · 2026-04-23T15:56:41Z

+	flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck
+	flag.Set("stderrthreshold", "INFO")                   //nolint:errcheck


Same concern as in main.go: ignoring flag.Set errors can lead to silently incorrect logging behavior. Please handle the errors (fail fast or log a warning) to avoid a hard-to-diagnose operational regression if the flags aren’t present/registered as expected.

Suggested change

flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck

flag.Set("stderrthreshold", "INFO") //nolint:errcheck

if err := flag.Set("legacy_stderr_threshold_behavior", "false"); err != nil {

klog.Fatalf("Failed to set legacy_stderr_threshold_behavior: %v", err)

}

if err := flag.Set("stderrthreshold", "INFO"); err != nil {

klog.Fatalf("Failed to set stderrthreshold: %v", err)

}

Fixed — same treatment applied here: both flag.Set calls now check for errors and klog.Fatalf on failure.

Copilot · 2026-04-23T15:56:41Z

 func main() {
 	utilfeature.DefaultMutableFeatureGate.AddFlag(pflag.CommandLine)
 	klog.InitFlags(nil)
+	// Opt into the new klog behavior so that -stderrthreshold is honored even
+	// when -logtostderr=true (the default).
+	// Ref: kubernetes/klog#212, kubernetes/klog#432
+	flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck
+	flag.Set("stderrthreshold", "INFO")                   //nolint:errcheck


The same multi-line comment and flag-defaulting logic is duplicated in two entrypoints. To avoid drift (e.g., one binary missing a future tweak), consider extracting a small helper (e.g., initKlogFlags() in a shared package) called by both mains.

Suggested change

func main() {

utilfeature.DefaultMutableFeatureGate.AddFlag(pflag.CommandLine)

klog.InitFlags(nil)

// Opt into the new klog behavior so that -stderrthreshold is honored even

// when -logtostderr=true (the default).

// Ref: kubernetes/klog#212, kubernetes/klog#432

flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck

flag.Set("stderrthreshold", "INFO") //nolint:errcheck

func initKlogFlags() {

klog.InitFlags(nil)

// Opt into the new klog behavior so that -stderrthreshold is honored even

// when -logtostderr=true (the default).

// Ref: kubernetes/klog#212, kubernetes/klog#432

flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck

flag.Set("stderrthreshold", "INFO") //nolint:errcheck

}

func main() {

utilfeature.DefaultMutableFeatureGate.AddFlag(pflag.CommandLine)

initKlogFlags()

Good suggestion. Since these are two separate main packages (main.go and cmd/daemon/main.go), extracting a shared helper would require introducing a new internal package — which feels like scope creep for this PR. The duplication is minimal (4 lines) and the pattern is now consistent between both entrypoints. Happy to revisit if the maintainers prefer a shared helper.

Replace //nolint:errcheck suppressions with proper error handling. Both flag.Set calls now fail fast via klog.Fatalf if the flag cannot be set, making misconfiguration immediately visible. Signed-off-by: Pierluigi Lenoci <pierluigilenoci@gmail.com>

Copilot AI review requested due to automatic review settings April 23, 2026 15:41

kruise-bot requested a review from FillZpp April 23, 2026 15:41

kruise-bot requested a review from zmberg April 23, 2026 15:41

kruise-bot added the size/S size/S 10-29 label Apr 23, 2026

Copilot AI reviewed Apr 23, 2026

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Copilot started reviewing on behalf of pierluigilenoci April 23, 2026 16:13 View session

pierluigilenoci mentioned this pull request Apr 24, 2026

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

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fix: honor -stderrthreshold when -logtostderr is set#2421

fix: honor -stderrthreshold when -logtostderr is set#2421
pierluigilenoci wants to merge 2 commits intoopenkruise:masterfrom
pierluigilenoci:fix/honor-stderrthreshold

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		flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck
		flag.Set("stderrthreshold", "INFO") //nolint:errcheck

-	flag.Set("legacy_stderr_threshold_behavior", "false") //nolint:errcheck
-	flag.Set("stderrthreshold", "INFO")                   //nolint:errcheck
+	if err := flag.Set("legacy_stderr_threshold_behavior", "false"); err != nil {
+		klog.Fatalf("failed to set flag %q: %v", "legacy_stderr_threshold_behavior", err)
+	}
+	if err := flag.Set("stderrthreshold", "INFO"); err != nil {
+		klog.Fatalf("failed to set flag %q: %v", "stderrthreshold", err)
+	}

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pierluigilenoci commented Apr 23, 2026

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