Add "server-feature-gates" flag.

pkg/featuregate/feature_gate.go

@@ -16,6 +16,7 @@
 package featuregate
 
 import (
+	"flag"
 	"fmt"
 	"sort"
 	"strconv"
@@ -30,7 +31,7 @@ import (
 type Feature string
 
 const (
-	flagName = "feature-gates"
+	defaultFlagName = "feature-gates"
 
 	// allAlphaGate is a global toggle for alpha features. Per-feature key
 	// values override the default set by allAlphaGate. Examples:
@@ -98,7 +99,7 @@ type MutableFeatureGate interface {
 	FeatureGate
 
 	// AddFlag adds a flag for setting global feature gates to the specified FlagSet.
-	AddFlag(fs *pflag.FlagSet)
+	AddFlag(fs *flag.FlagSet, flagName string)
 	// Set parses and stores flag gates for known features
 	// from a string like feature1=true,feature2=false,...
 	Set(value string) error
@@ -165,6 +166,9 @@ func setUnsetBetaGates(known map[Feature]FeatureSpec, enabled map[Feature]bool,
 var _ pflag.Value = &featureGate{}
 
 func New(name string, lg *zap.Logger) *featureGate {
+	if lg == nil {
+		lg = zap.NewNop()
+	}
 	known := map[Feature]FeatureSpec{}
 	for k, v := range defaultFeatures {
 		known[k] = v
@@ -349,7 +353,10 @@ func (f *featureGate) Enabled(key Feature) bool {
 }
 
 // AddFlag adds a flag for setting global feature gates to the specified FlagSet.
-func (f *featureGate) AddFlag(fs *pflag.FlagSet) {
+func (f *featureGate) AddFlag(fs *flag.FlagSet, flagName string) {
+	if flagName == "" {
+		flagName = defaultFlagName
+	}
 	f.lock.Lock()
 	// TODO(mtaufen): Shouldn't we just close it on the first Set/SetFromMap instead?
 	// Not all components expose a feature gates flag using this AddFlag method, and

pkg/featuregate/feature_gate_test.go

@@ -15,11 +15,11 @@
 package featuregate
 
 import (
+	"flag"
 	"fmt"
 	"strings"
 	"testing"
 
-	"github.com/spf13/pflag"
 	"github.com/stretchr/testify/assert"
 	"go.uber.org/zap/zaptest"
 )
@@ -203,15 +203,15 @@ func TestFeatureGateFlag(t *testing.T) {
 	}
 	for i, test := range tests {
 		t.Run(test.arg, func(t *testing.T) {
-			fs := pflag.NewFlagSet("testfeaturegateflag", pflag.ContinueOnError)
+			fs := flag.NewFlagSet("testfeaturegateflag", flag.ContinueOnError)
 			f := New("test", zaptest.NewLogger(t))
 			f.Add(map[Feature]FeatureSpec{
 				testAlphaGate: {Default: false, PreRelease: Alpha},
 				testBetaGate:  {Default: false, PreRelease: Beta},
 			})
-			f.AddFlag(fs)
+			f.AddFlag(fs, defaultFlagName)
 
-			err := fs.Parse([]string{fmt.Sprintf("--%s=%s", flagName, test.arg)})
+			err := fs.Parse([]string{fmt.Sprintf("--%s=%s", defaultFlagName, test.arg)})
 			if test.parseError != "" {
 				if !strings.Contains(err.Error(), test.parseError) {
 					t.Errorf("%d: Parse() Expected %v, Got %v", i, test.parseError, err)
@@ -603,8 +603,8 @@ func TestFeatureGateOverrideDefault(t *testing.T) {
 
 	t.Run("returns error if already added to flag set", func(t *testing.T) {
 		f := New("test", zaptest.NewLogger(t))
-		fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
-		f.AddFlag(fs)
+		fs := flag.NewFlagSet("test", flag.ContinueOnError)
+		f.AddFlag(fs, defaultFlagName)
 
 		if err := f.OverrideDefault("TestFeature", true); err == nil {
 			t.Error("expected a non-nil error to be returned")

server/embed/config.go

@@ -42,6 +42,7 @@ import (
 	"go.etcd.io/etcd/client/pkg/v3/transport"
 	"go.etcd.io/etcd/client/pkg/v3/types"
 	clientv3 "go.etcd.io/etcd/client/v3"
+	"go.etcd.io/etcd/pkg/v3/featuregate"
 	"go.etcd.io/etcd/pkg/v3/flags"
 	"go.etcd.io/etcd/pkg/v3/netutil"
 	"go.etcd.io/etcd/server/v3/config"
@@ -50,6 +51,7 @@ import (
 	"go.etcd.io/etcd/server/v3/etcdserver/api/rafthttp"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v3compactor"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v3discovery"
+	"go.etcd.io/etcd/server/v3/features"
 )
 
 const (
@@ -108,6 +110,8 @@ const (
 	maxElectionMs = 50000
 	// backend freelist map type
 	freelistArrayType = "array"
+
+	ServerFeatureGateFlagName = "feature-gates"
 )
 
 var (
@@ -455,6 +459,9 @@ type Config struct {
 
 	// V2Deprecation describes phase of API & Storage V2 support
 	V2Deprecation config.V2DeprecationEnum `json:"v2-deprecation"`
+
+	// ServerFeatureGate is a server level feature gate
+	ServerFeatureGate featuregate.FeatureGate
 }
 
 // configYAML holds the config suitable for yaml parsing
@@ -576,6 +583,7 @@ func NewConfig() *Config {
 		},
 
 		AutoCompactionMode: DefaultAutoCompactionMode,
+		ServerFeatureGate:  features.NewDefaultServerFeatureGate(DefaultName, nil),
 	}
 	cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
 	return cfg
@@ -762,6 +770,9 @@ func (cfg *Config) AddFlags(fs *flag.FlagSet) {
 	// unsafe
 	fs.BoolVar(&cfg.UnsafeNoFsync, "unsafe-no-fsync", false, "Disables fsync, unsafe, will cause data loss.")
 	fs.BoolVar(&cfg.ForceNewCluster, "force-new-cluster", false, "Force to create a new one member cluster.")
+
+	// featuregate
+	cfg.ServerFeatureGate.(featuregate.MutableFeatureGate).AddFlag(fs, ServerFeatureGateFlagName)
 }
 
 func ConfigFromFile(path string) (*Config, error) {

server/embed/etcd.go

@@ -228,6 +228,7 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 		ExperimentalMaxLearners:                       cfg.ExperimentalMaxLearners,
 		V2Deprecation:                                 cfg.V2DeprecationEffective(),
 		ExperimentalLocalAddress:                      cfg.InferLocalAddr(),
+		ServerFeatureGate:                             cfg.ServerFeatureGate,
 	}
 
 	if srvcfg.ExperimentalEnableDistributedTracing {

server/etcdmain/config_test.go

@@ -25,8 +25,10 @@ import (
 
 	"sigs.k8s.io/yaml"
 
+	"go.etcd.io/etcd/pkg/v3/featuregate"
 	"go.etcd.io/etcd/pkg/v3/flags"
 	"go.etcd.io/etcd/server/v3/embed"
+	"go.etcd.io/etcd/server/v3/features"
 )
 
 func TestConfigParsingMemberFlags(t *testing.T) {
@@ -395,6 +397,55 @@ func TestFlagsPresentInHelp(t *testing.T) {
 	})
 }
 
+func TestParseFeatureGateFlags(t *testing.T) {
+	testCases := []struct {
+		name             string
+		args             []string
+		expectErr        bool
+		expectedFeatures map[featuregate.Feature]bool
+	}{
+		{
+			name: "default",
+			expectedFeatures: map[featuregate.Feature]bool{
+				features.DistributedTracing:      false,
+				features.StopGRPCServiceOnDefrag: false,
+			},
+		},
+		{
+			name: "can set feature gate flag",
+			args: []string{
+				"--experimental-stop-grpc-service-on-defrag=false",
+				fmt.Sprintf("--%s=DistributedTracing=true,StopGRPCServiceOnDefrag=true", embed.ServerFeatureGateFlagName),
+			},
+			expectedFeatures: map[featuregate.Feature]bool{
+				features.DistributedTracing:      true,
+				features.StopGRPCServiceOnDefrag: true,
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			cfg := newConfig()
+			err := cfg.parse(tc.args)
+			if tc.expectErr {
+				if err == nil {
+					t.Fatal("expect parse error")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			for k, v := range tc.expectedFeatures {
+				if cfg.ec.ServerFeatureGate.Enabled(k) != v {
+					t.Errorf("expected feature gate %s=%v, got %v", k, v, cfg.ec.ServerFeatureGate.Enabled(k))
+				}
+			}
+		})
+	}
+}
+
 func mustCreateCfgFile(t *testing.T, b []byte) *os.File {
 	tmpfile, err := os.CreateTemp("", "servercfg")
 	if err != nil {

server/etcdmain/help.go

@@ -18,12 +18,14 @@ package etcdmain
 import (
 	"fmt"
 	"strconv"
+	"strings"
 
 	"golang.org/x/crypto/bcrypt"
 
 	cconfig "go.etcd.io/etcd/server/v3/config"
 	"go.etcd.io/etcd/server/v3/embed"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/rafthttp"
+	"go.etcd.io/etcd/server/v3/features"
 )
 
 var (
@@ -103,6 +105,8 @@ Member:
     Read timeout set on each rafthttp connection
   --raft-write-timeout '` + rafthttp.DefaultConnWriteTimeout.String() + `'
     Write timeout set on each rafthttp connection
+  --feature-gates ''
+    A set of key=value pairs that describe server level feature gates for alpha/experimental features. Options are:` + "\n    " + strings.Join(features.NewDefaultServerFeatureGate("", nil).KnownFeatures(), "\n    ") + `
 
 Clustering:
   --initial-advertise-peer-urls 'http://localhost:2380'

server/features/etcd_features.go

@@ -0,0 +1,63 @@
+// Copyright 2024 The etcd 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 features
+
+import (
+	"fmt"
+
+	"go.uber.org/zap"
+
+	"go.etcd.io/etcd/pkg/v3/featuregate"
+)
+
+const (
+	// Every feature gate should add method here following this template:
+	//
+	// // owner: @username
+	// // kep: https://kep.k8s.io/NNN (or issue: https://github.com/etcd-io/etcd/issues/NNN, or main PR: https://github.com/etcd-io/etcd/pull/NNN)
+	// // alpha: v3.X
+	// MyFeature featuregate.Feature = "MyFeature"
+	//
+	// Feature gates should be listed in alphabetical, case-sensitive
+	// (upper before any lower case character) order. This reduces the risk
+	// of code conflicts because changes are more likely to be scattered
+	// across the file.
+
+	// DistributedTracing enables experimental distributed  tracing using OpenTelemetry Tracing.
+	// owner: @dashpole
+	// alpha: v3.5
+	// issue: https://github.com/etcd-io/etcd/issues/12460
+	DistributedTracing featuregate.Feature = "DistributedTracing"
+	// StopGRPCServiceOnDefrag enables etcd gRPC service to stop serving client requests on defragmentation.
+	// owner: @chaochn47
+	// alpha: v3.6
+	// main PR: https://github.com/etcd-io/etcd/pull/18279
+	StopGRPCServiceOnDefrag featuregate.Feature = "StopGRPCServiceOnDefrag"
+)
+
+var (
+	DefaultEtcdServerFeatureGates = map[featuregate.Feature]featuregate.FeatureSpec{
+		DistributedTracing:      {Default: false, PreRelease: featuregate.Alpha},
+		StopGRPCServiceOnDefrag: {Default: false, PreRelease: featuregate.Alpha},
+	}
+)
+
+func NewDefaultServerFeatureGate(name string, lg *zap.Logger) featuregate.FeatureGate {
+	fg := featuregate.New(fmt.Sprintf("%sServerFeatureGate", name), lg)
+	if err := fg.Add(DefaultEtcdServerFeatureGates); err != nil {
+		panic(err)
+	}
+	return fg
+}