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fix: honor -stderrthreshold flag in klog v2 #3086

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fix: honor -stderrthreshold flag in klog v2 #3086

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dd45656
fix: honor -stderrthreshold flag in klog v2
pierluigilenoci Apr 24, 2026
c69a14e
fix: use correct flag values for stderrthreshold fix
pierluigilenoci Apr 24, 2026
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7 changes: 7 additions & 0 deletions cmd/controller-manager/app/options/common.go
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Original file line number Diff line number Diff line change
Expand Up @@ -157,6 +157,13 @@ func InitGOPS() error {
func AddKlogFlags(fs *pflag.FlagSet) {
local := flag.NewFlagSet("klog", flag.ExitOnError)
klog.InitFlags(local)

// Opt into the new klog behavior so that -stderrthreshold is honored even
// when -logtostderr=true (the default).
// Ref: kubernetes/klog#212, kubernetes/klog#432
_ = local.Set("legacy_stderr_threshold_behavior", "false")
_ = local.Set("stderrthreshold", "INFO")
Comment on lines +164 to +165
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@gemini-code-assist gemini-code-assist Bot Apr 24, 2026

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medium

The errors returned by local.Set are being ignored. While it's unlikely to fail in this case, it's a good practice to handle errors during application initialization. A failure to set these flags would lead to incorrect logging behavior that could be difficult to debug. Consider checking the error and logging a fatal error if setting the flag fails, to ensure the application exits if it cannot be configured correctly.

	if err := local.Set("logtostderr", "false"); err != nil {
		klog.Fatalf("failed to set klog logtostderr flag: %v", err)
	}
	if err := local.Set("legacy_stderr_threshold_behavior", "true"); err != nil {
		klog.Fatalf("failed to set klog legacy_stderr_threshold_behavior flag: %v", err)
	}


local.VisitAll(func(fl *flag.Flag) {
fl.Name = strings.ReplaceAll(fl.Name, "_", "-")
fs.AddGoFlag(fl)
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7 changes: 7 additions & 0 deletions cmd/kk/app/options/other.go
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Expand Up @@ -158,6 +158,13 @@ func InitGOPS() error {
func AddKlogFlags(fs *pflag.FlagSet) {
local := flag.NewFlagSet("klog", flag.ExitOnError)
klog.InitFlags(local)

// Opt into the new klog behavior so that -stderrthreshold is honored even
// when -logtostderr=true (the default).
// Ref: kubernetes/klog#212, kubernetes/klog#432
_ = local.Set("legacy_stderr_threshold_behavior", "false")
_ = local.Set("stderrthreshold", "INFO")
Comment on lines +165 to +166
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@gemini-code-assist gemini-code-assist Bot Apr 24, 2026

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medium

The errors returned by local.Set are being ignored. While it's unlikely to fail in this case, it's a good practice to handle errors during application initialization. A failure to set these flags would lead to incorrect logging behavior that could be difficult to debug. Consider checking the error and logging a fatal error if setting the flag fails, to ensure the application exits if it cannot be configured correctly.

	if err := local.Set("logtostderr", "false"); err != nil {
		klog.Fatalf("failed to set klog logtostderr flag: %v", err)
	}
	if err := local.Set("legacy_stderr_threshold_behavior", "true"); err != nil {
		klog.Fatalf("failed to set klog legacy_stderr_threshold_behavior flag: %v", err)
	}


local.VisitAll(func(fl *flag.Flag) {
fl.Name = strings.ReplaceAll(fl.Name, "_", "-")
fs.AddGoFlag(fl)
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2 changes: 1 addition & 1 deletion go.mod
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Expand Up @@ -30,7 +30,7 @@ require (
k8s.io/apiserver v0.35.0
k8s.io/client-go v0.35.0
k8s.io/component-base v0.35.0
k8s.io/klog/v2 v2.130.1
k8s.io/klog/v2 v2.140.0
k8s.io/utils v0.0.0-20251002143259-bc988d571ff4
oras.land/oras-go/v2 v2.6.0
sigs.k8s.io/cluster-api v1.9.2
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4 changes: 2 additions & 2 deletions go.sum
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Original file line number Diff line number Diff line change
Expand Up @@ -460,8 +460,8 @@ k8s.io/cluster-bootstrap v0.31.3 h1:O1Yxk1bLaxZvmQCXLaJjj5iJD+lVMfJdRUuKgbUHPlA=
k8s.io/cluster-bootstrap v0.31.3/go.mod h1:TI6TCsQQB4FfcryWgNO3SLXSKWBqHjx4DfyqSFwixj8=
k8s.io/component-base v0.35.0 h1:+yBrOhzri2S1BVqyVSvcM3PtPyx5GUxCK2tinZz1G94=
k8s.io/component-base v0.35.0/go.mod h1:85SCX4UCa6SCFt6p3IKAPej7jSnF3L8EbfSyMZayJR0=
k8s.io/klog/v2 v2.130.1 h1:n9Xl7H1Xvksem4KFG4PYbdQCQxqc/tTUyrgXaOhHSzk=
k8s.io/klog/v2 v2.130.1/go.mod h1:3Jpz1GvMt720eyJH1ckRHK1EDfpxISzJ7I9OYgaDtPE=
k8s.io/klog/v2 v2.140.0 h1:Tf+J3AH7xnUzZyVVXhTgGhEKnFqye14aadWv7bzXdzc=
k8s.io/klog/v2 v2.140.0/go.mod h1:o+/RWfJ6PwpnFn7OyAG3QnO47BFsymfEfrz6XyYSSp0=
k8s.io/kube-openapi v0.0.0-20250910181357-589584f1c912 h1:Y3gxNAuB0OBLImH611+UDZcmKS3g6CthxToOb37KgwE=
k8s.io/kube-openapi v0.0.0-20250910181357-589584f1c912/go.mod h1:kdmbQkyfwUagLfXIad1y2TdrjPFWp2Q89B3qkRwf/pQ=
k8s.io/utils v0.0.0-20251002143259-bc988d571ff4 h1:SjGebBtkBqHFOli+05xYbK8YF1Dzkbzn+gDM4X9T4Ck=
Expand Down