Allow e2e test to pick up test VM image using image family

test/e2e/metriconly/e2e_npd_test.go

@@ -38,6 +38,7 @@ const junitFileName = "junit.xml"
 var zone = flag.String("zone", "", "gce zone the hosts live in")
 var project = flag.String("project", "", "gce project the hosts live in")
 var image = flag.String("image", "", "image to test")
+var imageFamily = flag.String("image-family", "", "image family to pick up the test image. Ignored when -image is set.")
 var imageProject = flag.String("image-project", "", "gce project of the OS image")
 var jobName = flag.String("job-name", "", "name of the Prow job running the test")
 var sshKey = flag.String("ssh-key", "", "path to ssh private key.")

test/e2e/metriconly/metrics_test.go

@@ -37,6 +37,15 @@ var _ = ginkgo.Describe("NPD should export Prometheus metrics.", func() {
 		var err error
 		// TODO(xueweiz): Creating instance for each test case is slow. We should either reuse the instance
 		// between tests, or have a way to run these tests in parallel.
+		if *imageFamily != "" && *image == "" {
+			gceImage, err := computeService.Images.GetFromFamily(*imageProject, *imageFamily).Do()
+			if err != nil {
+				ginkgo.Fail(fmt.Sprintf("Unable to get image from family %s at project %s: %v",
+					*imageFamily, *imageProject, err))
+			}
+			*image = gceImage.Name
+			fmt.Printf("Using image %s from image family %s at project %s\n", *image, *imageFamily, *imageProject)
+		}
 		instance, err = gce.CreateInstance(
 			gce.Instance{
 				Name:           "npd-metrics-" + *image + "-" + uuid.NewUUID().String()[:8],