fix(server): enforce listen-metrics-urls client TLS info when its scheme is https/unixs

server/embed/etcd.go

@@ -822,6 +822,24 @@ func (e *Etcd) pickGRPCGatewayServeContext(splitHTTP bool) *serveCtx {
 	panic("Expect at least one context able to serve grpc")
 }
 
+var ErrMissingClientTLSInfoForMetricsURL = errors.New("client TLS key/cert (--cert-file, --key-file) must be provided for metrics url")
+
+func (e *Etcd) createMetricsListener(murl url.URL) (net.Listener, error) {
+	tlsInfo := &e.cfg.ClientTLSInfo
+	switch murl.Scheme {
+	case "http":
+		tlsInfo = nil
+	case "https", "unixs":
+		if e.cfg.ClientTLSInfo.Empty() {
+			return nil, ErrMissingClientTLSInfoForMetricsURL
+		}
+	}
+	return transport.NewListenerWithOpts(murl.Host, murl.Scheme,
+		transport.WithTLSInfo(tlsInfo),
+		transport.WithSocketOpts(&e.cfg.SocketOpts),
+	)
+}
+
 func (e *Etcd) serveMetrics() (err error) {
 	if e.cfg.Metrics == "extensive" {
 		grpc_prometheus.EnableHandlingTimeHistogram()
@@ -833,14 +851,7 @@ func (e *Etcd) serveMetrics() (err error) {
 		etcdhttp.HandleHealth(e.cfg.logger, metricsMux, e.Server)
 
 		for _, murl := range e.cfg.ListenMetricsUrls {
-			tlsInfo := &e.cfg.ClientTLSInfo
-			if murl.Scheme == "http" {
-				tlsInfo = nil
-			}
-			ml, err := transport.NewListenerWithOpts(murl.Host, murl.Scheme,
-				transport.WithTLSInfo(tlsInfo),
-				transport.WithSocketOpts(&e.cfg.SocketOpts),
-			)
+			ml, err := e.createMetricsListener(murl)
 			if err != nil {
 				return err
 			}

server/embed/etcd_test.go

@@ -0,0 +1,38 @@
+// 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 embed
+
+import (
+	"net/url"
+	"testing"
+
+	"go.etcd.io/etcd/client/pkg/v3/transport"
+)
+
+func TestEmptyClientTLSInfo_createMetricsListener(t *testing.T) {
+	e := &Etcd{
+		cfg: Config{
+			ClientTLSInfo: transport.TLSInfo{},
+		},
+	}
+
+	murl := url.URL{
+		Scheme: "https",
+		Host:   "localhost:8080",
+	}
+	if _, err := e.createMetricsListener(murl); err != ErrMissingClientTLSInfoForMetricsURL {
+		t.Fatalf("expected error %v, got %v", ErrMissingClientTLSInfoForMetricsURL, err)
+	}
+}

server/etcdmain/help.go

@@ -238,7 +238,7 @@ Profiling and Monitoring:
   --metrics 'basic'
     Set level of detail for exported metrics, specify 'extensive' to include server side grpc histogram metrics.
   --listen-metrics-urls ''
-    List of URLs to listen on for the metrics and health endpoints.
+    List of URLs to listen on for the /metrics and /health endpoints. For https, the client URL TLS info is used.
 
 Logging:
   --logger 'zap'

tests/e2e/etcd_config_test.go

@@ -28,6 +28,7 @@ import (
 	"golang.org/x/sync/errgroup"
 
 	"go.etcd.io/etcd/pkg/v3/expect"
+	"go.etcd.io/etcd/server/v3/embed"
 	"go.etcd.io/etcd/tests/v3/framework/config"
 	"go.etcd.io/etcd/tests/v3/framework/e2e"
 )
@@ -120,6 +121,60 @@ func TestEtcdUnixPeers(t *testing.T) {
 	}
 }
 
+// TestEtcdListenMetricsURLsWithMissingClientTLSInfo checks that the HTTPs listen metrics URL
+// but without the client TLS info will fail its verification.
+func TestEtcdListenMetricsURLsWithMissingClientTLSInfo(t *testing.T) {
+	e2e.SkipInShortMode(t)
+
+	tempDir := t.TempDir()
+	defer os.RemoveAll(tempDir)
+
+	caFile, certFiles, keyFiles, err := generateCertsForIPs(tempDir, []net.IP{net.ParseIP("127.0.0.1")})
+	require.NoError(t, err)
+
+	// non HTTP but metrics URL is HTTPS, invalid when the client TLS info is not provided
+	clientURL := fmt.Sprintf("http://localhost:%d", e2e.EtcdProcessBasePort)
+	peerURL := fmt.Sprintf("https://localhost:%d", e2e.EtcdProcessBasePort+1)
+	listenMetricsURL := fmt.Sprintf("https://localhost:%d", e2e.EtcdProcessBasePort+2)
+
+	commonArgs := []string{
+		e2e.BinPath.Etcd,
+		"--name", "e0",
+		"--data-dir", tempDir,
+
+		"--listen-client-urls", clientURL,
+		"--advertise-client-urls", clientURL,
+
+		"--initial-advertise-peer-urls", peerURL,
+		"--listen-peer-urls", peerURL,
+
+		"--initial-cluster", "e0=" + peerURL,
+
+		"--listen-metrics-urls", listenMetricsURL,
+
+		"--peer-cert-file", certFiles[0],
+		"--peer-key-file", keyFiles[0],
+		"--peer-trusted-ca-file", caFile,
+		"--peer-client-cert-auth",
+	}
+
+	proc, err := e2e.SpawnCmd(commonArgs, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := proc.Stop(); err != nil {
+			t.Error(err)
+		}
+		proc.Wait() // ensure the port has been released
+		_ = proc.Close()
+	}()
+
+	if err := e2e.WaitReadyExpectProc(context.TODO(), proc, []string{embed.ErrMissingClientTLSInfoForMetricsURL.Error()}); err != nil {
+		t.Fatal(err)
+	}
+}
+
 // TestEtcdPeerCNAuth checks that the inter peer auth based on CN of cert is working correctly.
 func TestEtcdPeerCNAuth(t *testing.T) {
 	e2e.SkipInShortMode(t)