add gc metrics and collect sync errors

pkg/controller/garbagecollector/metrics/metrics.go

@@ -0,0 +1,45 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package metrics
+
+import (
+	"sync"
+
+	"k8s.io/component-base/metrics"
+	"k8s.io/component-base/metrics/legacyregistry"
+)
+
+const GarbageCollectorControllerSubsystem = "garbagecollector_controller"
+
+var (
+	GarbageCollectorResourcesSyncError = metrics.NewCounter(
+		&metrics.CounterOpts{
+			Subsystem:      GarbageCollectorControllerSubsystem,
+			Name:           "resources_sync_error_total",
+			Help:           "Number of garbage collector resources sync errors",
+			StabilityLevel: metrics.ALPHA,
+		})
+)
+
+var registerMetrics sync.Once
+
+// Register registers GarbageCollectorController metrics.
+func Register() {
+	registerMetrics.Do(func() {
+		legacyregistry.MustRegister(GarbageCollectorResourcesSyncError)
+	})
+}