Add config file field for feature-gates flag.

Signed-off-by: Siyuan Zhang <sizhang@google.com>

server/embed/config.go

@@ -483,6 +483,8 @@ type configJSON struct {
 
 	ClientSecurityJSON securityConfig `json:"client-transport-security"`
 	PeerSecurityJSON   securityConfig `json:"peer-transport-security"`
+
+	ServerFeatureGatesJSON string `json:"feature-gates"`
 }
 
 type securityConfig struct {
@@ -796,6 +798,13 @@ func (cfg *configYAML) configFromFile(path string) error {
 		return err
 	}
 
+	if cfg.configJSON.ServerFeatureGatesJSON != "" {
+		err = cfg.Config.ServerFeatureGate.(featuregate.MutableFeatureGate).Set(cfg.configJSON.ServerFeatureGatesJSON)
+		if err != nil {
+			return err
+		}
+	}
+
 	if cfg.configJSON.ListenPeerURLs != "" {
 		u, err := types.NewURLs(strings.Split(cfg.configJSON.ListenPeerURLs, ","))
 		if err != nil {

server/embed/config_test.go

@@ -31,6 +31,8 @@ import (
 	"go.etcd.io/etcd/client/pkg/v3/srv"
 	"go.etcd.io/etcd/client/pkg/v3/transport"
 	"go.etcd.io/etcd/client/pkg/v3/types"
+	"go.etcd.io/etcd/pkg/v3/featuregate"
+	"go.etcd.io/etcd/server/v3/features"
 )
 
 func notFoundErr(service, domain string) error {
@@ -89,6 +91,78 @@ func TestConfigFileOtherFields(t *testing.T) {
 	assert.Equal(t, false, cfg.SocketOpts.ReuseAddress, "ReuseAddress does not match")
 }
 
+func TestConfigFileFeatureGates(t *testing.T) {
+	testCases := []struct {
+		name                   string
+		serverFeatureGatesJSON string
+		expectErr              bool
+		expectedFeatures       map[featuregate.Feature]bool
+	}{
+		{
+			name: "default",
+			expectedFeatures: map[featuregate.Feature]bool{
+				features.DistributedTracing:      false,
+				features.StopGRPCServiceOnDefrag: false,
+			},
+		},
+		{
+			name:                   "set StopGRPCServiceOnDefrag to true",
+			serverFeatureGatesJSON: "StopGRPCServiceOnDefrag=true",
+			expectedFeatures: map[featuregate.Feature]bool{
+				features.DistributedTracing:      false,
+				features.StopGRPCServiceOnDefrag: true,
+			},
+		},
+		{
+			name:                   "set both features to true",
+			serverFeatureGatesJSON: "DistributedTracing=true,StopGRPCServiceOnDefrag=true",
+			expectedFeatures: map[featuregate.Feature]bool{
+				features.DistributedTracing:      true,
+				features.StopGRPCServiceOnDefrag: true,
+			},
+		},
+		{
+			name:                   "error setting unrecognized feature",
+			serverFeatureGatesJSON: "DistributedTracing=true,StopGRPCServiceOnDefragExp=true",
+			expectErr:              true,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			yc := struct {
+				ExperimentalStopGRPCServiceOnDefrag *bool  `json:"experimental-stop-grpc-service-on-defrag,omitempty"`
+				ServerFeatureGatesJSON              string `json:"feature-gates"`
+			}{
+				ServerFeatureGatesJSON: tc.serverFeatureGatesJSON,
+			}
+
+			b, err := yaml.Marshal(&yc)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			tmpfile := mustCreateCfgFile(t, b)
+			defer os.Remove(tmpfile.Name())
+
+			cfg, err := ConfigFromFile(tmpfile.Name())
+			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.ServerFeatureGate.Enabled(k) != v {
+					t.Errorf("expected feature gate %s=%v, got %v", k, v, cfg.ServerFeatureGate.Enabled(k))
+				}
+			}
+		})
+	}
+}
+
 // TestUpdateDefaultClusterFromName ensures that etcd can start with 'etcd --name=abc'.
 func TestUpdateDefaultClusterFromName(t *testing.T) {
 	cfg := NewConfig()