fix(server/embed): enforce non-empty client TLS if scheme is https/unixs

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

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 +1,24 @@
+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'