kubelet/metrics: fix multiple Register call

DRA also calls Register at pkg/kubelet/cm/container_manager_linux.go NewContainerManager(), causing volume stats collector being ignored.
Fix this by moving it out of `sync.Once()`, allowing multiple calls to `Register()` func.

Author: huww98

pkg/kubelet/cm/container_manager_linux.go

@@ -317,7 +317,7 @@ func NewContainerManager(mountUtil mount.Interface, cadvisorInterface cadvisor.I
 		if err != nil {
 			return nil, err
 		}
-		metrics.Register(cm.draManager.NewMetricsCollector())
+		metrics.RegisterCollectors(cm.draManager.NewMetricsCollector())
 	}
 	cm.kubeClient = kubeClient
 

pkg/kubelet/kubelet.go

@@ -1632,7 +1632,8 @@ func (kl *Kubelet) StartGarbageCollection() {
 // Note that the modules here must not depend on modules that are not initialized here.
 func (kl *Kubelet) initializeModules(ctx context.Context) error {
 	// Prometheus metrics.
-	metrics.Register(
+	metrics.Register()
+	metrics.RegisterCollectors(
 		collectors.NewVolumeStatsCollector(kl),
 		collectors.NewLogMetricsCollector(kl.StatsProvider.ListPodStats),
 	)

pkg/kubelet/metrics/metrics.go

@@ -1194,7 +1194,7 @@ var (
 var registerMetrics sync.Once
 
 // Register registers all metrics.
-func Register(collectors ...metrics.StableCollector) {
+func Register() {
 	// Register the metrics.
 	registerMetrics.Do(func() {
 		legacyregistry.MustRegister(FirstNetworkPodStartSLIDuration)
@@ -1274,8 +1274,6 @@ func Register(collectors ...metrics.StableCollector) {
 		legacyregistry.MustRegister(OrphanPodCleanedVolumes)
 		legacyregistry.MustRegister(OrphanPodCleanedVolumesErrors)
 
-		legacyregistry.CustomMustRegister(collectors...)
-
 		if utilfeature.DefaultFeatureGate.Enabled(features.GracefulNodeShutdown) &&
 			utilfeature.DefaultFeatureGate.Enabled(features.GracefulNodeShutdownBasedOnPodPriority) {
 			legacyregistry.MustRegister(GracefulShutdownStartTime)
@@ -1312,6 +1310,10 @@ func Register(collectors ...metrics.StableCollector) {
 	})
 }
 
+func RegisterCollectors(collectors ...metrics.StableCollector) {
+	legacyregistry.CustomMustRegister(collectors...)
+}
+
 // GetGather returns the gatherer. It used by test case outside current package.
 func GetGather() metrics.Gatherer {
 	return legacyregistry.DefaultGatherer