From 2bd2be7439f79ef9a8d27c67c87709a0cf93835c 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 | 15 ++++++++++++---
 server/etcdserver/metrics.go    |  9 +++++++++
 server/etcdserver/server.go     |  2 ++
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/pkg/featuregate/feature_gate.go b/pkg/featuregate/feature_gate.go
index c899616d92a6..a10733351b75 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"
 )
@@ -113,7 +114,7 @@ type MutableFeatureGate interface {
 	// GetAll returns a copy of the map of known feature names to feature specs.
 	GetAll() map[Feature]FeatureSpec
 	// AddMetrics adds feature enablement metrics
-	AddMetrics()
+	AddMetrics(gaugeVec *prometheus.GaugeVec)
 	// 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/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)