fix: opt into fixed klog stderrthreshold behavior

[pierluigilenoci]

Problem

klog v2 defaults -logtostderr to true. When this flag is active, the -stderrthreshold flag is silently ignored — all log messages of every severity (INFO, WARNING, ERROR, FATAL) are unconditionally written to stderr.

This makes it impossible for log-aggregation systems (Fluentd, Fluent Bit, Loki, Datadog, etc.) to filter logs by severity on the stderr stream.

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

Fix

klog v2.140.0 introduced a new legacy_stderr_threshold_behavior flag (kubernetes/klog#432). Setting it to false makes -stderrthreshold work correctly even when -logtostderr=true.

This PR opts pluto into the fixed behavior by setting legacy_stderr_threshold_behavior=false after klog.InitFlags() in cmd/root.go. The default stderrthreshold remains INFO so the observable behavior is unchanged — all logs still go to stderr by default. Users who want filtering can now pass -stderrthreshold=WARNING or -stderrthreshold=ERROR and it will actually take effect.

References

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

[CLAassistant]

All committers have signed the CLA.

[pierluigilenoci]

recheck

[pierluigilenoci]

Gentle ping — could you take a look when you get a chance? All CI checks are green (the Publish Dev Orb failure is a known fork limitation, also present on other fork PRs like #589 and #581). This opts into the fixed klog stderrthreshold behavior per kubernetes/klog#212. Happy to address any feedback. Thank you!

[pierluigilenoci]

Hi team — friendly follow-up. All CI checks are green except Publish Dev Orb, which is a known CircleCI fork limitation (same failure pattern seen on other fork PRs like #589 and #581).

This is a small change to opt into klog's fixed stderrthreshold behavior. Would appreciate a review when you get a chance. Thank you!

[pierluigilenoci]

Hi @sudermanjr — friendly ping on this PR. It opts into the fixed klog stderrthreshold behavior. Happy to address any feedback. Thanks!

[pierluigilenoci]

Hi @transient1, @jdesouza — I see you're both active contributors on Pluto (and @transient1 is listed in CODEOWNERS). Would you be able to take a look at this PR when you get a chance? Happy to make any changes if needed. Thanks!