From 8b805646e2ebfe673fef7327a383e5ab2fe1e740 Mon Sep 17 00:00:00 2001
From: Gang Li <ganglica@google.com>
Date: Wed, 19 Feb 2025 23:28:53 +0000
Subject: [PATCH] add prometheus metric

Signed-off-by: Gang Li <ganglica@google.com>
---
 pkg/featuregate/feature_gate.go      | 17 +++++++---
 pkg/featuregate/feature_gate_test.go | 48 ++++++++++++++++++++++++++++
 server/etcdserver/metrics.go         |  9 ++++++
 server/etcdserver/server.go          |  2 ++
 4 files changed, 72 insertions(+), 4 deletions(-)

diff --git a/pkg/featuregate/feature_gate.go b/pkg/featuregate/feature_gate.go
index c899616d92a6..9c2bb24c6f77 100644
--- a/pkg/featuregate/feature_gate.go
+++ b/pkg/featuregate/feature_gate.go
@@ -25,6 +25,7 @@ import (
 	"sync"
 	"sync/atomic"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/spf13/pflag"
 	"go.uber.org/zap"
 )
@@ -94,6 +95,8 @@ type FeatureGate interface {
 	DeepCopy() MutableFeatureGate
 	// String returns a string containing all enabled feature gates, formatted as "key1=value1,key2=value2,...".
 	String() string
+	// AddMetrics adds feature enablement metrics
+	AddMetrics(gaugeVec *prometheus.GaugeVec)
 }
 
 // MutableFeatureGate parses and stores flag gates for known features from
@@ -112,8 +115,6 @@ type MutableFeatureGate interface {
 	Add(features map[Feature]FeatureSpec) error
 	// GetAll returns a copy of the map of known feature names to feature specs.
 	GetAll() map[Feature]FeatureSpec
-	// AddMetrics adds feature enablement metrics
-	AddMetrics()
 	// OverrideDefault sets a local override for the registered default value of a named
 	// feature. If the feature has not been previously registered (e.g. by a call to Add), has a
 	// locked default, or if the gate has already registered itself with a FlagSet, a non-nil
@@ -363,8 +364,16 @@ func (f *featureGate) AddFlag(fs *flag.FlagSet, flagName string) {
 		"Options are:\n"+strings.Join(known, "\n"))
 }
 
-func (f *featureGate) AddMetrics() {
-	// TODO(henrybear327): implement this.
+func (f *featureGate) AddMetrics(gaugeVec *prometheus.GaugeVec) {
+	for Feature, FeatureSpec := range f.GetAll() {
+		var metricVal float64
+		if f.Enabled(Feature) {
+			metricVal = 1
+		} else {
+			metricVal = 0
+		}
+		gaugeVec.With(prometheus.Labels{"name": string(Feature), "stage": string(FeatureSpec.PreRelease)}).Set(metricVal)
+	}
 }
 
 // KnownFeatures returns a slice of strings describing the FeatureGate's known features.
diff --git a/pkg/featuregate/feature_gate_test.go b/pkg/featuregate/feature_gate_test.go
index 5dc5a86537d7..d8f42d04c756 100644
--- a/pkg/featuregate/feature_gate_test.go
+++ b/pkg/featuregate/feature_gate_test.go
@@ -20,6 +20,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/zap/zaptest"
@@ -555,3 +556,50 @@ func TestFeatureGateOverrideDefault(t *testing.T) {
 		assert.Errorf(t, err, "expected a non-nil error to be returned")
 	})
 }
+
+func TestAddMetric(t *testing.T) {
+
+	etcdServerFeatureEnabled = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: "etcd",
+			Subsystem: "server",
+			Name:      "etcd_server_feature_enabled",
+			Help:      "Whether or not a feature is enabled. 1 is enabled, 0 is not.",
+		},
+		[]string{"name", "stage"},
+	)
+
+	const testAlphaGate Feature = "TestAlpha"
+	const testBetaGate Feature = "TestBeta"
+	const testGAGate Feature = "TestGA"
+
+	featuremap := map[Feature]FeatureSpec{
+		testGAGate:    {Default: true, PreRelease: GA},
+		testAlphaGate: {Default: false, PreRelease: Alpha},
+		testBetaGate:  {Default: false, PreRelease: Beta},
+	}
+
+	expectedMetrics := []metricValue{
+		{featureName: "TestAlpha", preRelease: "Alpha", value: 1},
+		{featureName: "TestBeta", preRelease: "Beta", value: 1},
+		{featureName: "TestGA", preRelease: "GA", value: 0},
+	}
+
+	f := New("test", zaptest.NewLogger(t))
+	f.Add(featuremap)
+	f.SetFromMap(map[string]bool{"testAlphaGate": true})
+
+	type metricValue struct {
+		featureName string
+		preRelease  string
+		value       float64
+	}
+
+	f.AddMetric(etcdServerFeatureEnabled)
+
+	for _, expected := range expectedMetrics {
+		gotVal, err := etcdServerFeatureEnabled.GetMetricWithLabelValues(expected.featureName, expected.preRelease)
+		require.NoError(t, err)
+		require.Equal(t, expected.value, gotVal)
+	}
+}
diff --git a/server/etcdserver/metrics.go b/server/etcdserver/metrics.go
index 5f3c2f51368f..e48e820a5917 100644
--- a/server/etcdserver/metrics.go
+++ b/server/etcdserver/metrics.go
@@ -140,6 +140,15 @@ var (
 		},
 		[]string{"server_id"},
 	)
+	etcdServerFeatureEnabled = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: "etcd",
+			Subsystem: "server",
+			Name:      "etcd_server_feature_enabled",
+			Help:      "Whether or not a feature is enabled. 1 is enabled, 0 is not.",
+		},
+		[]string{"name", "stage"},
+	)
 	fdUsed = prometheus.NewGauge(prometheus.GaugeOpts{
 		Namespace: "os",
 		Subsystem: "fd",
diff --git a/server/etcdserver/server.go b/server/etcdserver/server.go
index 2c45553bc833..b8238b99efc2 100644
--- a/server/etcdserver/server.go
+++ b/server/etcdserver/server.go
@@ -342,6 +342,8 @@ func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
 		firstCommitInTerm:     notify.NewNotifier(),
 		clusterVersionChanged: notify.NewNotifier(),
 	}
+
+	cfg.ServerFeatureGate.(featuregate.MutableFeatureGate).AddMetrics(etcdServerFeatureEnabled)
 	serverID.With(prometheus.Labels{"server_id": b.cluster.nodeID.String()}).Set(1)
 	srv.cluster.SetVersionChangedNotifier(srv.clusterVersionChanged)