add a feature enabled metric

Change-Id: Id872651c4219d4749fc4227da7d944e883e4e355

staging/src/k8s.io/component-base/metrics/prometheus/feature/metrics.go

@@ -0,0 +1,51 @@
+/*
+Copyright 2022 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 feature
+
+import (
+	"context"
+	"fmt"
+
+	k8smetrics "k8s.io/component-base/metrics"
+	"k8s.io/component-base/metrics/legacyregistry"
+)
+
+var (
+	// featureEnabled is a Prometheus Gauge metrics used for recording the enablement of a k8s feature.
+	featureEnabled = k8smetrics.NewGaugeVec(
+		&k8smetrics.GaugeOpts{
+			Namespace:      "k8s",
+			Name:           "feature_enabled",
+			Help:           "This metric records the result of whether a feature is enabled.",
+			StabilityLevel: k8smetrics.ALPHA,
+		},
+		[]string{"name", "enabled"},
+	)
+)
+
+func init() {
+	legacyregistry.MustRegister(featureEnabled)
+}
+
+func ResetFeatureEnabledMetric() {
+	featureEnabled.Reset()
+}
+
+func RecordFeatureEnabled(ctx context.Context, name string, enabled bool) error {
+	featureEnabled.WithContext(ctx).WithLabelValues(name, fmt.Sprintf("%v", enabled)).Set(1)
+	return nil
+}

staging/src/k8s.io/component-base/metrics/prometheus/feature/metrics_test.go

@@ -0,0 +1,77 @@
+/*
+Copyright 2022 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 feature
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"k8s.io/component-base/metrics/legacyregistry"
+	"k8s.io/component-base/metrics/testutil"
+)
+
+var (
+	testedMetrics = []string{"k8s_feature_enabled"}
+)
+
+func TestObserveHealthcheck(t *testing.T) {
+	defer legacyregistry.Reset()
+	defer ResetFeatureEnabledMetric()
+
+	testCases := []struct {
+		desc    string
+		name    string
+		enabled bool
+		want    string
+	}{
+		{
+			desc:    "test enabled",
+			name:    "feature-a",
+			enabled: true,
+			want: `
+       	# HELP k8s_feature_enabled [ALPHA] This metric records the result of whether a feature is enabled.
+        # TYPE k8s_feature_enabled gauge
+        k8s_feature_enabled{enabled="true",name="feature-a"} 1
+`,
+		},
+		{
+			desc:    "test disabled",
+			name:    "feature-b",
+			enabled: false,
+			want: `
+       	# HELP k8s_feature_enabled [ALPHA] This metric records the result of whether a feature is enabled.
+        # TYPE k8s_feature_enabled gauge
+        k8s_feature_enabled{enabled="false",name="feature-b"} 1
+`,
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			defer ResetFeatureEnabledMetric()
+			err := RecordFeatureEnabled(context.Background(), test.name, test.enabled)
+			if err != nil {
+				t.Errorf("unexpected err: %v", err)
+			}
+
+			if err := testutil.GatherAndCompare(legacyregistry.DefaultGatherer, strings.NewReader(test.want), testedMetrics...); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}