embed: make v2 endpoint optional

Documentation/op-guide/configuration.md

@@ -140,6 +140,12 @@ To start etcd automatically using custom settings at startup in Linux, using a [
 + default: 0
 + env variable: ETCD_AUTO_COMPACTION_RETENTION
 
+
+### --enable-v2
++ Accept etcd V2 client requests
++ default: true
++ env variable: ETCD_ENABLE_V2
+
 ## Proxy flags
 
 `--proxy` prefix flags configures etcd to run in [proxy mode][proxy]. "proxy" supports v2 API only.

embed/config.go

@@ -102,6 +102,7 @@ type Config struct {
 	InitialCluster      string `json:"initial-cluster"`
 	InitialClusterToken string `json:"initial-cluster-token"`
 	StrictReconfigCheck bool   `json:"strict-reconfig-check"`
+	EnableV2            bool   `json:"enable-v2"`
 
 	// security
 
@@ -175,6 +176,7 @@ func NewConfig() *Config {
 		InitialClusterToken: "etcd-cluster",
 		StrictReconfigCheck: true,
 		Metrics:             "basic",
+		EnableV2:            true,
 	}
 	cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
 	return cfg

embed/etcd.go

@@ -319,15 +319,18 @@ func (e *Etcd) serve() (err error) {
 	}
 
 	// Start a client server goroutine for each listen address
-	ch := http.Handler(&cors.CORSHandler{
-		Handler: v2http.NewClientHandler(e.Server, e.Server.Cfg.ReqTimeout()),
-		Info:    e.cfg.CorsInfo,
-	})
+	var v2h http.Handler
+	if e.Config().EnableV2 {
+		v2h = http.Handler(&cors.CORSHandler{
+			Handler: v2http.NewClientHandler(e.Server, e.Server.Cfg.ReqTimeout()),
+			Info:    e.cfg.CorsInfo,
+		})
+	}
 	for _, sctx := range e.sctxs {
 		// read timeout does not work with http close notify
 		// TODO: https://github.com/golang/go/issues/9524
 		go func(s *serveCtx) {
-			e.errc <- s.serve(e.Server, ctlscfg, ch, e.errc)
+			e.errc <- s.serve(e.Server, ctlscfg, v2h, e.errc)
 		}(sctx)
 	}
 	return nil

embed/serve.go

@@ -122,6 +122,11 @@ func (sctx *serveCtx) serve(s *etcdserver.EtcdServer, tlscfg *tls.Config, handle
 // grpcHandlerFunc returns an http.Handler that delegates to grpcServer on incoming gRPC
 // connections or otherHandler otherwise. Copied from cockroachdb.
 func grpcHandlerFunc(grpcServer *grpc.Server, otherHandler http.Handler) http.Handler {
+	if otherHandler == nil {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			grpcServer.ServeHTTP(w, r)
+		})
+	}
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.ProtoMajor == 2 && strings.Contains(r.Header.Get("Content-Type"), "application/grpc") {
 			grpcServer.ServeHTTP(w, r)
@@ -181,7 +186,9 @@ func (sctx *serveCtx) createMux(gwmux *gw.ServeMux, handler http.Handler) *http.
 	}
 
 	httpmux.Handle("/v3alpha/", gwmux)
-	httpmux.Handle("/", handler)
+	if handler != nil {
+		httpmux.Handle("/", handler)
+	}
 	return httpmux
 }
 

etcd.conf.yml.sample

@@ -69,6 +69,9 @@ initial-cluster-state: 'new'
 # Reject reconfiguration requests that would cause quorum loss.
 strict-reconfig-check: false
 
+# Accept etcd V2 client requests
+enable-v2: true
+
 # Valid values include 'on', 'readonly', 'off'
 proxy: 'off'
 

etcdmain/config.go

@@ -155,6 +155,7 @@ func newConfig() *config {
 		plog.Panicf("unexpected error setting up clusterStateFlag: %v", err)
 	}
 	fs.BoolVar(&cfg.StrictReconfigCheck, "strict-reconfig-check", cfg.StrictReconfigCheck, "Reject reconfiguration requests that would cause quorum loss.")
+	fs.BoolVar(&cfg.EnableV2, "enable-v2", true, "Accept etcd V2 client requests.")
 
 	// proxy
 	fs.Var(cfg.proxy, "proxy", fmt.Sprintf("Valid values include %s", strings.Join(cfg.proxy.Values, ", ")))

etcdmain/help.go

@@ -88,6 +88,8 @@ clustering flags:
 		reject reconfiguration requests that would cause quorum loss.
 	--auto-compaction-retention '0'
 		auto compaction retention in hour. 0 means disable auto compaction.
+	--enable-v2
+		Accept etcd V2 client requests.
 
 proxy flags:
 	"proxy" supports v2 API only.