Export zone locality in outbound destination metrics (#13129)

Currently, we don't have a simple way of checking if the endpoint a proxy is discovering is in the same zone or not.

This adds a "zone_locality" metric label to the outbound destination address metrics. Note that this does not increase the cardinality of the related metrics, as this label doesn't vary within an endpoint.

Validated by checking the prometheus metrics on a local cluster and verifying this label appears in the outbound transport metrics.

Signed-off-by: Scott Fleener <[email protected]>

Author: sfleen

controller/api/destination/endpoint_translator.go

@@ -444,6 +444,7 @@ func (et *endpointTranslator) sendClientAdd(set watcher.AddressSet) {
 				Addr:              addr,
 				Weight:            defaultWeight,
 				AuthorityOverride: authOverride,
+				MetricLabels:      map[string]string{},
 			}
 
 			if address.Identity != "" {
@@ -465,12 +466,20 @@ func (et *endpointTranslator) sendClientAdd(set watcher.AddressSet) {
 			}
 		}
 
-		if et.extEndpointZoneWeights {
-			// EXPERIMENTAL: Use the endpoint weight field to indicate zonal
-			// preference so that local endoints are more heavily weighted.
-			if et.nodeTopologyZone != "" && address.Zone != nil && *address.Zone == et.nodeTopologyZone {
-				wa.Weight *= 10
+		if et.nodeTopologyZone != "" && address.Zone != nil {
+			if *address.Zone == et.nodeTopologyZone {
+				wa.MetricLabels["zone_locality"] = "local"
+
+				if et.extEndpointZoneWeights {
+					// EXPERIMENTAL: Use the endpoint weight field to indicate zonal
+					// preference so that local endoints are more heavily weighted.
+					wa.Weight *= 10
+				}
+			} else {
+				wa.MetricLabels["zone_locality"] = "remote"
 			}
+		} else {
+			wa.MetricLabels["zone_locality"] = "unknown"
 		}
 
 		addrs = append(addrs, wa)

controller/api/destination/endpoint_translator_test.go

@@ -485,6 +485,7 @@ func TestEndpointTranslatorForPods(t *testing.T) {
 			"serviceaccount":        "serviceaccount-name",
 			"control_plane_ns":      "linkerd",
 			"zone":                  "",
+			"zone_locality":         "unknown",
 		}
 		if diff := deep.Equal(actualAddedAddress1MetricLabels, expectedAddedAddress1MetricLabels); diff != nil {
 			t.Fatalf("Expected global metric labels sent to be [%v] but was [%v]", expectedAddedAddress1MetricLabels, actualAddedAddress1MetricLabels)
@@ -658,6 +659,7 @@ func TestEndpointTranslatorExternalWorkloads(t *testing.T) {
 		expectedAddedAddress1MetricLabels := map[string]string{
 			"external_workload": "ew-1",
 			"zone":              "",
+			"zone_locality":     "unknown",
 			"workloadgroup":     "wg-name",
 		}
 		if diff := deep.Equal(actualAddedAddress1MetricLabels, expectedAddedAddress1MetricLabels); diff != nil {