cmd: silence warnings in kube-controller-manager/kube-apiserver, dedupe/color warnings in kubectl

cmd/kube-apiserver/app/server.go

@@ -53,6 +53,7 @@ import (
 	"k8s.io/apiserver/pkg/util/webhook"
 	clientgoinformers "k8s.io/client-go/informers"
 	clientgoclientset "k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
 	"k8s.io/client-go/util/keyutil"
 	cloudprovider "k8s.io/cloud-provider"
 	cliflag "k8s.io/component-base/cli/flag"
@@ -100,6 +101,12 @@ cluster's shared state through which all other components interact.`,
 
 		// stop printing usage when the command errors
 		SilenceUsage: true,
+		PersistentPreRunE: func(*cobra.Command, []string) error {
+			// silence client-go warnings.
+			// kube-apiserver loopback clients should not log self-issued warnings.
+			rest.SetDefaultWarningHandler(rest.NoWarnings{})
+			return nil
+		},
 		RunE: func(cmd *cobra.Command, args []string) error {
 			verflag.PrintAndExitIfRequested()
 			cliflag.PrintFlags(cmd.Flags())