feat: Add support for endpoint topology routing hints

docs/endpointslice-metrics.md

@@ -5,6 +5,6 @@
 | kube_endpointslice_annotations | Gauge | `endpointslice`=&lt;endpointslice-name&gt; <br> `namespace`=&lt;endpointslice-namespace&gt; <br> `annotation_ENDPOINTSLICE_ANNOTATION`=&lt;ENDPOINTSLICE_ANNOTATION&gt;  | EXPERIMENTAL |
 | kube_endpointslice_info | Gauge | `endpointslice`=&lt;endpointslice-name&gt; <br> `namespace`=&lt;endpointslice-namespace&gt;  | EXPERIMENTAL |
 | kube_endpointslice_ports | Gauge | `endpointslice`=&lt;endpointslice-name&gt; <br> `namespace`=&lt;endpointslice-namespace&gt; <br> `port_name`=&lt;endpointslice-port-name&gt; <br> `port_protocol`=&lt;endpointslice-port-protocol&gt; <br> `port_number`=&lt;endpointslice-port-number&gt; | EXPERIMENTAL |
-| kube_endpointslice_endpoints | Gauge | `endpointslice`=&lt;endpointslice-name&gt; <br> `namespace`=&lt;endpointslice-namespace&gt; <br> `ready`=&lt;endpointslice-ready&gt; <br> `serving`=&lt;endpointslice-serving&gt; <br> `terminating`=&lt;endpointslice-terminating&gt; <br> `hostname`=&lt;endpointslice-hostname&gt; <br> `targetref_kind`=&lt;endpointslice-targetref-kind&gt; <br> `targetref_name`=&lt;endpointslice-targetref-name&gt; <br> `targetref_namespace`=&lt;endpointslice-targetref-namespace&gt; <br> `nodename`=&lt;endpointslice-nodename&gt; <br> `endpoint_zone`=&lt;endpointslice-zone&gt;  | EXPERIMENTAL |
+| kube_endpointslice_endpoints | Gauge | `endpointslice`=&lt;endpointslice-name&gt; <br> `namespace`=&lt;endpointslice-namespace&gt; <br> `ready`=&lt;endpointslice-ready&gt; <br> `serving`=&lt;endpointslice-serving&gt; <br> `terminating`=&lt;endpointslice-terminating&gt; <br> `hostname`=&lt;endpointslice-hostname&gt; <br> `targetref_kind`=&lt;endpointslice-targetref-kind&gt; <br> `targetref_name`=&lt;endpointslice-targetref-name&gt; <br> `targetref_namespace`=&lt;endpointslice-targetref-namespace&gt; <br> `nodename`=&lt;endpointslice-nodename&gt; <br> `endpoint_zone`=&lt;endpointslice-zone&gt; <br> `hint`=&lt;topology-aware-routing-hint&gt; | EXPERIMENTAL |
 | kube_endpointslice_labels | Gauge | `endpointslice`=&lt;endpointslice-name&gt; <br> `namespace`=&lt;endpointslice-namespace&gt; <br> `label_ENDPOINTSLICE_LABEL`=&lt;ENDPOINTSLICE_LABEL&gt;  | EXPERIMENTAL |
 | kube_endpointslice_created | Gauge | `endpointslice`=&lt;endpointslice-name&gt; <br> `namespace`=&lt;endpointslice-namespace&gt; | EXPERIMENTAL |

internal/store/endpointslice.go

@@ -134,11 +134,30 @@ func endpointSliceMetricFamilies(allowAnnotationsList, allowLabelsList []string)
 					for _, address := range ep.Addresses {
 						newlabelValues := make([]string, len(labelValues))
 						copy(newlabelValues, labelValues)
-						m = append(m, &metric.Metric{
-							LabelKeys:   labelKeys,
-							LabelValues: append(newlabelValues, address),
-							Value:       1,
-						})
+						newlabelValues = append(newlabelValues, address)
+
+						// Hint is populated when the endpoint is configured to be zone aware and preferentially route requests to its local zone.
+						if ep.Hints != nil && len(ep.Hints.ForZones) > 0 {
+
+							// Because each endpoint can have multiple zones, we need to create a metric for each zone.
+							// and we need to make sure we aren't adding the hint label repeatedly, we need to copy the array
+							for _, zone := range ep.Hints.ForZones {
+								zoneLabelValues := make([]string, len(newlabelValues))
+								copy(zoneLabelValues, newlabelValues)
+								zoneLabelValues = append(zoneLabelValues, zone.Name)
+								m = append(m, &metric.Metric{
+									LabelKeys:   append(labelKeys, "hint"),
+									LabelValues: zoneLabelValues,
+									Value:       1,
+								})
+							}
+						} else {
+							m = append(m, &metric.Metric{
+								LabelKeys:   labelKeys,
+								LabelValues: newlabelValues,
+								Value:       1,
+							})
+						}
 					}
 				}
 				return &metric.Family{

internal/store/endpointslice_test.go

@@ -122,6 +122,41 @@ func TestEndpointSliceStore(t *testing.T) {
 				"kube_endpointslice_endpoints",
 			},
 		},
+		{
+			Obj: &discoveryv1.EndpointSlice{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: "test_endpointslice-endpoints",
+				},
+				AddressType: "IPv4",
+				Endpoints: []discoveryv1.Endpoint{
+					{
+						NodeName: &nodename,
+						Conditions: discoveryv1.EndpointConditions{
+							Ready:       &ready,
+							Terminating: &terminating,
+						},
+						Hostname:  &hostname,
+						Zone:      &zone,
+						Addresses: addresses,
+						Hints: &discoveryv1.EndpointHints{
+							ForZones: []discoveryv1.ForZone{
+								{Name: "zone1"},
+							},
+						},
+					},
+				},
+			},
+			Want: `
+					# HELP kube_endpointslice_endpoints Endpoints attached to the endpointslice.
+					# TYPE kube_endpointslice_endpoints gauge
+					kube_endpointslice_endpoints{address="10.0.0.1",endpoint_nodename="node",endpoint_zone="west",endpointslice="test_endpointslice-endpoints",hostname="host",ready="true",terminating="false",hint="zone1"} 1
+					kube_endpointslice_endpoints{address="192.168.1.10",endpoint_nodename="node",endpoint_zone="west",endpointslice="test_endpointslice-endpoints",hostname="host",ready="true",terminating="false",hint="zone1"} 1
+				  `,
+
+			MetricNames: []string{
+				"kube_endpointslice_endpoints",
+			},
+		},
 		{
 			AllowAnnotationsList: []string{
 				"foo",