Send update when pod's IP address is empty

When the pod gets evicted, its IP address becomes empty and it needs to
be removed from the targets.

discovery/kubernetes/pod.go

@@ -170,14 +170,14 @@ func podLabels(pod *apiv1.Pod) model.LabelSet {
 }
 
 func (p *Pod) buildPod(pod *apiv1.Pod) *targetgroup.Group {
-	// During startup the pod may not have an IP yet. This does not even allow
-	// for an up metric, so we skip the target.
-	if len(pod.Status.PodIP) == 0 {
-		return nil
-	}
 	tg := &targetgroup.Group{
 		Source: podSource(pod),
 	}
+	// PodIP can be empty when a pod is starting or has been evicted.
+	if len(pod.Status.PodIP) == 0 {
+		return tg
+	}
+
 	tg.Labels = podLabels(pod)
 	tg.Labels[namespaceLabel] = lv(pod.Namespace)
 

discovery/kubernetes/pod_test.go

@@ -350,3 +350,46 @@ func TestPodDiscoveryUpdate(t *testing.T) {
 		},
 	}.Run(t)
 }
+
+func TestPodDiscoveryUpdateEmptyPodIP(t *testing.T) {
+	n, i := makeTestPodDiscovery()
+	initialPod := makePod()
+
+	updatedPod := makePod()
+	updatedPod.Status.PodIP = ""
+
+	i.GetStore().Add(initialPod)
+
+	k8sDiscoveryTest{
+		discovery:  n,
+		afterStart: func() { go func() { i.Update(updatedPod) }() },
+		expectedInitial: []*targetgroup.Group{
+			{
+				Targets: []model.LabelSet{
+					{
+						"__address__":                                   "1.2.3.4:9000",
+						"__meta_kubernetes_pod_container_name":          "testcontainer",
+						"__meta_kubernetes_pod_container_port_name":     "testport",
+						"__meta_kubernetes_pod_container_port_number":   "9000",
+						"__meta_kubernetes_pod_container_port_protocol": "TCP",
+					},
+				},
+				Labels: model.LabelSet{
+					"__meta_kubernetes_pod_name":      "testpod",
+					"__meta_kubernetes_namespace":     "default",
+					"__meta_kubernetes_pod_node_name": "testnode",
+					"__meta_kubernetes_pod_ip":        "1.2.3.4",
+					"__meta_kubernetes_pod_host_ip":   "2.3.4.5",
+					"__meta_kubernetes_pod_ready":     "true",
+					"__meta_kubernetes_pod_uid":       "abc123",
+				},
+				Source: "pod/default/testpod",
+			},
+		},
+		expectedRes: []*targetgroup.Group{
+			{
+				Source: "pod/default/testpod",
+			},
+		},
+	}.Run(t)
+}