xds: add MetricsReporter for generic xds client

xds/internal/clients/config.go

@@ -100,3 +100,13 @@ type Locality struct {
 	// SubZone is the further subdivision within a zone.
 	SubZone string
 }
+
+// MetricsReporter is used by the XDSClient to report metrics.
+type MetricsReporter interface {
+	// ReportMetric reports a metric. The metric will be one of the predefined
+	// set of types depending on the client (XDSClient or LRSClient).
+	//
+	// Each client will produce different metrics. Please see the client's
+	// documentation for a list of possible metrics events.
+	ReportMetric(metric any)
+}

xds/internal/clients/xdsclient/authority.go

@@ -26,8 +26,10 @@ import (
 
 	"google.golang.org/grpc/grpclog"
 	igrpclog "google.golang.org/grpc/internal/grpclog"
+	"google.golang.org/grpc/xds/internal/clients"
 	"google.golang.org/grpc/xds/internal/clients/internal/syncutil"
 	"google.golang.org/grpc/xds/internal/clients/xdsclient/internal/xdsresource"
+	"google.golang.org/grpc/xds/internal/clients/xdsclient/metrics"
 	"google.golang.org/protobuf/types/known/anypb"
 	"google.golang.org/protobuf/types/known/timestamppb"
 
@@ -87,6 +89,7 @@ type authority struct {
 	xdsClientSerializerClose  func()                       // Function to close the above serializer.
 	logger                    *igrpclog.PrefixLogger       // Logger for this authority.
 	target                    string                       // The gRPC Channel target.
+	metricsReporter           clients.MetricsReporter
 
 	// The below defined fields must only be accessed in the context of the
 	// serializer callback, owned by this authority.
@@ -121,6 +124,7 @@ type authorityBuildOptions struct {
 	getChannelForADS xdsChannelForADS             // Function to acquire a reference to an xdsChannel
 	logPrefix        string                       // Prefix for logging
 	target           string                       // Target for the gRPC Channel that owns xDS Client/Authority
+	metricsReporter  clients.MetricsReporter      // Metrics reporter for the authority
 }
 
 // newAuthority creates a new authority instance with the provided
@@ -145,6 +149,7 @@ func newAuthority(args authorityBuildOptions) *authority {
 		logger:                    igrpclog.NewPrefixLogger(l, logPrefix),
 		resources:                 make(map[ResourceType]map[string]*resourceState),
 		target:                    args.target,
+		metricsReporter:           args.metricsReporter,
 	}
 
 	// Create an ordered list of xdsChannels with their server configs. The
@@ -363,6 +368,11 @@ func (a *authority) handleADSResourceUpdate(serverConfig *ServerConfig, rType Re
 		// On error, keep previous version of the resource. But update status
 		// and error.
 		if uErr.Err != nil {
+			if a.metricsReporter != nil {
+				a.metricsReporter.ReportMetric(&metrics.ResourceUpdateInvalid{
+					ServerURI: serverConfig.ServerIdentifier.ServerURI, ResourceType: rType.TypeName,
+				})
+			}
 			state.md.ErrState = md.ErrState
 			state.md.Status = md.Status
 			for watcher := range state.watchers {
@@ -378,6 +388,12 @@ func (a *authority) handleADSResourceUpdate(serverConfig *ServerConfig, rType Re
 			continue
 		}
 
+		if a.metricsReporter != nil {
+			a.metricsReporter.ReportMetric(&metrics.ResourceUpdateValid{
+				ServerURI: serverConfig.ServerIdentifier.ServerURI, ResourceType: rType.TypeName,
+			})
+		}
+
 		if state.deletionIgnored {
 			state.deletionIgnored = false
 			a.logger.Infof("A valid update was received for resource %q of type %q after previously ignoring a deletion", name, rType.TypeName)

xds/internal/clients/xdsclient/metrics/metrics.go

@@ -0,0 +1,42 @@
+/*
+ *
+ * Copyright 2025 gRPC 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 metrics defines all metrics that can be produced by an xDS client.
+// All calls to the MetricsRecorder by the xDS client will contain a struct
+// from this package passed by pointer.
+package metrics
+
+// ResourceUpdateValid is a metric to report a valid resource update from
+// the xDS management server for a given resource type.
+type ResourceUpdateValid struct {
+	ServerURI    string
+	ResourceType string
+}
+
+// ResourceUpdateInvalid is a metric to report an invalid resource update
+// from the xDS management server for a given resource type.
+type ResourceUpdateInvalid struct {
+	ServerURI    string
+	ResourceType string
+}
+
+// ServerFailure is a metric to report a server failure of the xDS
+// management server.
+type ServerFailure struct {
+	ServerURI string
+}

xds/internal/clients/xdsclient/test/helpers_test.go

@@ -20,6 +20,7 @@ package xdsclient_test
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"fmt"
 	"strconv"
@@ -29,12 +30,14 @@ import (
 
 	"google.golang.org/grpc/internal/grpctest"
 	"google.golang.org/grpc/xds/internal/clients/internal/pretty"
+	"google.golang.org/grpc/xds/internal/clients/internal/testutils"
 	"google.golang.org/grpc/xds/internal/clients/xdsclient"
 	"google.golang.org/grpc/xds/internal/clients/xdsclient/internal/xdsresource"
 	"google.golang.org/protobuf/proto"
 
 	v3listenerpb "github.com/envoyproxy/go-control-plane/envoy/config/listener/v3"
 	v3httppb "github.com/envoyproxy/go-control-plane/envoy/extensions/filters/network/http_connection_manager/v3"
+	"github.com/google/go-cmp/cmp"
 )
 
 type s struct {
@@ -262,3 +265,36 @@ func buildResourceName(typeName, auth, id string, ctxParams map[string]string) s
 		ContextParams: ctxParams,
 	}).String()
 }
+
+// testMetricsReporter is a MetricsReporter to be used in tests. It sends
+// recording events on channels and provides helpers to check if certain events
+// have taken place.
+type testMetricsReporter struct {
+	metricsCh *testutils.Channel
+}
+
+// newTestMetricsReporter returns a new testMetricsReporter.
+func newTestMetricsReporter() *testMetricsReporter {
+	return &testMetricsReporter{
+		metricsCh: testutils.NewChannelWithSize(1),
+	}
+}
+
+// waitForMetric waits for a metric to be recorded and verifies that the
+// recorded metrics data matches the expected metricsDataWant. Returns
+// an error if failed to wait or received wrong data.
+func (r *testMetricsReporter) waitForMetric(ctx context.Context, metricsDataWant any) error {
+	got, err := r.metricsCh.Receive(ctx)
+	if err != nil {
+		return fmt.Errorf("timeout waiting for int64Count")
+	}
+	if diff := cmp.Diff(got, metricsDataWant); diff != "" {
+		return fmt.Errorf("received unexpected metrics value (-got, +want): %v", diff)
+	}
+	return nil
+}
+
+// ReportMetric sends the metrics data to the metricsCh channel.
+func (r *testMetricsReporter) ReportMetric(m any) {
+	r.metricsCh.Send(m)
+}