fix(kuma-dp): allow to configure address of application to scrape

api/mesh/v1alpha1/metrics.proto

@@ -73,6 +73,9 @@ message PrometheusAggregateMetricsConfig {
   // If false then the application won't be scrapped. If nil, then it is treated
   // as true and kuma-dp scrapes metrics from the service.
   google.protobuf.BoolValue enabled = 4;
+
+  // Address on which a service expose HTTP endpoint with Prometheus metrics.
+  string address = 5;
 }
 
 // PrometheusEnvoyConfig defines filters that should be passed to Envoy

pkg/xds/bootstrap/generator.go

@@ -206,22 +206,14 @@ func (b *bootstrapGenerator) getMetricsConfig(
 	if err != nil {
 		return err
 	}
-
-	var address string
-	if b.enableLocalhostInboundCluster {
-		address = core_mesh.IPv4Loopback.String()
-	} else {
-		address = dataplane.Spec.GetNetworking().GetAddress()
-	}
-
 	if config != nil {
 		aggregateConfig := []AggregateMetricsConfig{}
 		for _, config := range config.GetAggregate() {
 			if config.GetEnabled() != nil && !config.GetEnabled().GetValue() {
 				continue
 			}
 			aggregateConfig = append(aggregateConfig, AggregateMetricsConfig{
-				Address: address,
+				Address: b.getMetricsAddress(config, dataplane),
 				Name:    config.Name,
 				Port:    config.Port,
 				Path:    config.Path,
@@ -232,6 +224,23 @@ func (b *bootstrapGenerator) getMetricsConfig(
 	return nil
 }
 
+func (b *bootstrapGenerator) getMetricsAddress(
+	metricsConfig *mesh_proto.PrometheusAggregateMetricsConfig,
+	dataplane *core_mesh.DataplaneResource,
+) string {
+	if metricsConfig.Address != "" {
+		return metricsConfig.Address
+	} else {
+		var address string
+		if b.enableLocalhostInboundCluster {
+			address = core_mesh.IPv4Loopback.String()
+		} else {
+			address = dataplane.Spec.GetNetworking().GetAddress()
+		}
+		return address
+	}
+}
+
 func (b *bootstrapGenerator) validateRequest(request types.BootstrapRequest) error {
 	if b.dpAuthEnabled && request.DataplaneToken == "" && request.DataplaneTokenPath == "" {
 		return DpTokenRequired

test/e2e_env/universal/observability/applications_metrics.go

@@ -58,6 +58,20 @@ metrics:
 func ApplicationsMetrics() {
 	const mesh = "applications-metrics"
 	const meshNoAggregate = "applications-metrics-no-aggregate"
+	const meshWithLocalhostBound = "applications-metrics-localhost-bound"
+
+	dpLocalhostBoundAggregateConfig := `
+metrics:
+  type: prometheus
+  conf:
+    aggregate:
+    - name: localhost-bound-not-exposed
+      port: 8080
+      path: "/localhost-bound-not-exposed"
+    - name: localhost-bound
+      port: 8080
+      address: "127.0.0.1"
+      path: "/localhost-bound"`
 
 	dpAggregateConfig := `
 metrics:
@@ -92,6 +106,7 @@ metrics:
 		err := NewClusterSetup().
 			Install(MeshWithMetricsEnabeld(meshNoAggregate)).
 			Install(MeshKubernetesAndMetricsAggregate(mesh)).
+			Install(MeshWithMetricsEnabeld(meshWithLocalhostBound)).
 			Install(TestServerUniversal("test-server", mesh,
 				WithTransparentProxy(true),
 				WithArgs([]string{"echo", "--instance", "test-server"}),
@@ -110,6 +125,12 @@ metrics:
 				WithServiceName("test-server-dp-metrics"),
 				WithAppendDataplaneYaml(dpAggregateConfig),
 			)).
+			Install(TestServerUniversal("test-server-dp-metrics-localhost", meshWithLocalhostBound,
+				WithTransparentProxy(true),
+				WithArgs([]string{"echo", "--instance", "test-server-dp-metrics-localhost", "--ip", "127.0.0.1"}),
+				WithServiceName("test-server-dp-metrics-localhost"),
+				WithAppendDataplaneYaml(dpLocalhostBoundAggregateConfig),
+			)).
 			Setup(env.Cluster)
 		Expect(err).ToNot(HaveOccurred())
 	})
@@ -118,6 +139,8 @@ metrics:
 		Expect(env.Cluster.DeleteMesh(mesh)).To(Succeed())
 		Expect(env.Cluster.DeleteMeshApps(meshNoAggregate)).To(Succeed())
 		Expect(env.Cluster.DeleteMesh(meshNoAggregate)).To(Succeed())
+		Expect(env.Cluster.DeleteMeshApps(meshWithLocalhostBound)).To(Succeed())
+		Expect(env.Cluster.DeleteMesh(meshWithLocalhostBound)).To(Succeed())
 	})
 
 	It("should scrape metrics defined in mesh and not fail when defined service doesn't exist", func() {
@@ -193,4 +216,26 @@ metrics:
 		// metric from envoy
 		Expect(stdout).To(ContainSubstring("envoy_server_concurrency"))
 	})
+
+	It("should allow to define and expose localhost bound server", func() {
+		// given
+		ip := env.Cluster.GetApp("test-server-dp-metrics-localhost").GetIP()
+
+		// when
+		stdout, _, err := env.Cluster.ExecWithRetries("", "", "test-server-dp-metrics-localhost",
+			"curl", "-v", "-m", "3", "--fail", "http://"+net.JoinHostPort(ip, "1234")+"/metrics?filter=concurrency")
+
+		// then
+		Expect(err).ToNot(HaveOccurred())
+		Expect(stdout).ToNot(BeNil())
+		Expect(stdout).To(ContainSubstring(string(expfmt.FmtText)))
+
+		// path doesn't have defined address
+		Expect(stdout).ToNot(ContainSubstring("localhost-bound-not-exposed"))
+
+		// exposed localhost bound service
+		Expect(stdout).To(ContainSubstring("localhost-bound"))
+		// metric from envoy
+		Expect(stdout).To(ContainSubstring("envoy_server_concurrency"))
+	})
 }