Retry dns-operator updates on conflicts

This uses the standard K8s retry pattern. It’s not the only place in
subctl where we need to do this, I’ll follow up with another PR to fix
the rest.

Fixes: #236
Signed-off-by: Stephen Kitt <skitt@redhat.com>
(cherry picked from commit 2afe090)

pkg/subctl/lighthouse/dns/ensure.go

@@ -28,6 +28,7 @@ import (
 	clientset "k8s.io/client-go/kubernetes"
 	clientsetifc "k8s.io/client-go/kubernetes/typed/apps/v1"
 	"k8s.io/client-go/rest"
+	"k8s.io/client-go/util/retry"
 
 	"github.com/submariner-io/submariner-operator/pkg/internal/cli"
 )
@@ -223,32 +224,30 @@ func setupOpenShift(status *cli.Status, clientSet *clientset.Clientset, repo str
 
 	// Update operator deployment
 	deployments := clientSet.AppsV1().Deployments("openshift-dns-operator")
-	if deployments == nil {
-		// Assume we're not on OpenShift
-		return nil
-	}
-	deployment, err := deployments.Get("dns-operator", metav1.GetOptions{})
-	if err != nil {
-		return err
-	}
-	if deployment == nil {
-		// Assume we're not on OpenShift
-		return nil
-	}
-	for i, container := range deployment.Spec.Template.Spec.Containers {
-		if container.Name == "dns-operator" {
-			deployment.Spec.Template.Spec.Containers[i].Image = repo + operatorImage + ":" + version
-			for j, env := range container.Env {
-				if env.Name == "IMAGE" {
-					deployment.Spec.Template.Spec.Containers[i].Env[j].Value = repo + openShiftCoreDNSImage + ":" + version
+	retryErr := retry.RetryOnConflict(retry.DefaultRetry, func() error {
+		deployment, err := deployments.Get("dns-operator", metav1.GetOptions{})
+		if errors.IsNotFound(err) {
+			// Assume we're not on OpenShift
+			return nil
+		} else if err != nil {
+			return err
+		}
+		for i, container := range deployment.Spec.Template.Spec.Containers {
+			if container.Name == "dns-operator" {
+				deployment.Spec.Template.Spec.Containers[i].Image = repo + operatorImage + ":" + version
+				for j, env := range container.Env {
+					if env.Name == "IMAGE" {
+						deployment.Spec.Template.Spec.Containers[i].Env[j].Value = repo + openShiftCoreDNSImage + ":" + version
+					}
 				}
+				status.QueueSuccessMessage("Updated DNS operator deployment")
 			}
-			status.QueueSuccessMessage("Updated DNS operator deployment")
 		}
-	}
-	_, err = deployments.Update(deployment)
-	if err != nil {
+		_, err = deployments.Update(deployment)
 		return err
+	})
+	if retryErr != nil {
+		return fmt.Errorf("Error updating dns-operator deployment: %v", retryErr)
 	}
 
 	// Scale DNS operator down and back up