Merge pull request #42717 from andrewsykim/support-host-ip-downward-api

Automatic merge from submit-queue

Support status.hostIP in downward API

**What this PR does / why we need it**:
Exposes pod's hostIP (node IP) via downward API. 

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: 
fixes https://github.com/kubernetes/kubernetes/issues/24657

**Special notes for your reviewer**:
Not sure if there's more documentation that's needed, please point me in the right direction and I will add some :)

test/e2e/common/downward_api.go

@@ -62,7 +62,7 @@ var _ = framework.KubeDescribe("Downward API", func() {
 		testDownwardAPI(f, podName, env, expectations)
 	})
 
-	It("should provide pod IP as an env var [Conformance]", func() {
+	It("should provide pod and host IP as an env var [Conformance]", func() {
 		podName := "downward-api-" + string(uuid.NewUUID())
 		env := []v1.EnvVar{
 			{
@@ -74,10 +74,20 @@ var _ = framework.KubeDescribe("Downward API", func() {
 					},
 				},
 			},
+			{
+				Name: "HOST_IP",
+				ValueFrom: &v1.EnvVarSource{
+					FieldRef: &v1.ObjectFieldSelector{
+						APIVersion: "v1",
+						FieldPath:  "status.hostIP",
+					},
+				},
+			},
 		}
 
 		expectations := []string{
 			"POD_IP=(?:\\d+)\\.(?:\\d+)\\.(?:\\d+)\\.(?:\\d+)",
+			"HOST_IP=(?:\\d+)\\.(?:\\d+)\\.(?:\\d+)\\.(?:\\d+)",
 		}
 
 		testDownwardAPI(f, podName, env, expectations)

test/fixtures/doc-yaml/user-guide/downward-api/dapi-pod.yaml

@@ -20,4 +20,8 @@ spec:
           valueFrom:
             fieldRef:
               fieldPath: status.podIP
+        - name: MY_HOST_IP
+          valueFrom:
+            fieldRef:
+               fieldPath: status.hostIP
   restartPolicy: Never