Validate image name for kubectl rolling-update NAME --image=IMAGE

Require distinct image from current one when starting a new
rolling-update, and exit with error if an existing in-progress update
is targeting a different image.

docs/man/man1/kubectl-rolling-update.1

@@ -36,7 +36,7 @@ existing replication controller and overwrite at least one (common) label in its
 
 .PP
 \fB\-\-image\fP=""
-    Image to use for upgrading the replication controller.  Can not be used with \-\-filename/\-f
+    Image to use for upgrading the replication controller. Must be distinct from the existing image (either new image or new image tag).  Can not be used with \-\-filename/\-f
 
 .PP
 \fB\-\-no\-headers\fP=false

docs/user-guide/kubectl/kubectl_rolling-update.md

@@ -72,7 +72,7 @@ $ kubectl rolling-update frontend --image=image:v2
       --deployment-label-key="deployment": The key to use to differentiate between two different controllers, default 'deployment'.  Only relevant when --image is specified, ignored otherwise
       --dry-run[=false]: If true, print out the changes that would be made, but don't actually make them.
   -f, --filename=[]: Filename or URL to file to use to create the new replication controller.
-      --image="": Image to use for upgrading the replication controller.  Can not be used with --filename/-f
+      --image="": Image to use for upgrading the replication controller. Must be distinct from the existing image (either new image or new image tag).  Can not be used with --filename/-f
       --no-headers[=false]: When using the default output, don't print headers.
   -o, --output="": Output format. One of: json|yaml|wide|name|go-template=...|go-template-file=...|jsonpath=...|jsonpath-file=... See golang template [http://golang.org/pkg/text/template/#pkg-overview] and jsonpath template [http://releases.k8s.io/HEAD/docs/user-guide/jsonpath.md].
       --output-version="": Output the formatted object with the given version (default api-version).
@@ -119,7 +119,7 @@ $ kubectl rolling-update frontend --image=image:v2
 
 * [kubectl](kubectl.md)	 - kubectl controls the Kubernetes cluster manager
 
-###### Auto generated by spf13/cobra on 9-Oct-2015
+###### Auto generated by spf13/cobra on 19-Oct-2015
 
 <!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
 [![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/docs/user-guide/kubectl/kubectl_rolling-update.md?pixel)]()

pkg/kubectl/cmd/rollingupdate.go

@@ -90,7 +90,7 @@ func NewCmdRollingUpdate(f *cmdutil.Factory, out io.Writer) *cobra.Command {
 	usage := "Filename or URL to file to use to create the new replication controller."
 	kubectl.AddJsonFilenameFlag(cmd, &options.Filenames, usage)
 	cmd.MarkFlagRequired("filename")
-	cmd.Flags().String("image", "", "Image to use for upgrading the replication controller.  Can not be used with --filename/-f")
+	cmd.Flags().String("image", "", "Image to use for upgrading the replication controller. Must be distinct from the existing image (either new image or new image tag).  Can not be used with --filename/-f")
 	cmd.MarkFlagRequired("image")
 	cmd.Flags().String("deployment-label-key", "deployment", "The key to use to differentiate between two different controllers, default 'deployment'.  Only relevant when --image is specified, ignored otherwise")
 	cmd.Flags().Bool("dry-run", false, "If true, print out the changes that would be made, but don't actually make them.")
@@ -235,8 +235,14 @@ func RunRollingUpdate(f *cmdutil.Factory, out io.Writer, cmd *cobra.Command, arg
 			return err
 		}
 		if newRc != nil {
+			if inProgressImage := newRc.Spec.Template.Spec.Containers[0].Image; inProgressImage != image {
+				return cmdutil.UsageError(cmd, "Found existing in-progress update to image (%s).\nEither continue in-progress update with --image=%s or rollback with --rollback", inProgressImage, inProgressImage)
+			}
 			fmt.Fprintf(out, "Found existing update in progress (%s), resuming.\n", newRc.Name)
 		} else {
+			if oldRc.Spec.Template.Spec.Containers[0].Image == image {
+				return cmdutil.UsageError(cmd, "Specified --image must be distinct from existing container image")
+			}
 			newRc, err = kubectl.CreateNewControllerFromCurrentController(client, cmdNamespace, oldName, newName, image, deploymentKey)
 			if err != nil {
 				return err