kubectl: show node label if defined

We are moving towards marking master nodes as tainted, and not
necessarily unschedulable.  Further now we encourage users to cordon
nodes, marking them unschedulable.

Thus the reliance on "Unschedulable" is not really a great indicator for
the master.

So, recognize the existing node 'role' markers, and surface them
where Unschedulable is (in the status).

We recognize:

 * a kubernetes.io/role label
 * a kubeadm.alpha.kubernetes.io/role label

Fix #33533

pkg/kubectl/describe.go

@@ -1789,6 +1789,7 @@ func (d *NodeDescriber) Describe(namespace, name string, describerSettings Descr
 func describeNode(node *api.Node, nodeNonTerminatedPodsList *api.PodList, events *api.EventList, canViewPods bool) (string, error) {
 	return tabbedString(func(out io.Writer) error {
 		fmt.Fprintf(out, "Name:\t%s\n", node.Name)
+		fmt.Fprintf(out, "Role:\t%s\n", findNodeRole(node))
 		printLabelsMultiline(out, "Labels", node.Labels)
 		printTaintsInAnnotationMultiline(out, "Taints", node.Annotations)
 		fmt.Fprintf(out, "CreationTimestamp:\t%s\n", node.CreationTimestamp.Time.Format(time.RFC1123Z))

pkg/kubectl/resource_printer.go

@@ -1491,6 +1491,10 @@ func printNode(node *api.Node, w io.Writer, options PrintOptions) error {
 	if node.Spec.Unschedulable {
 		status = append(status, "SchedulingDisabled")
 	}
+	role := findNodeRole(node)
+	if role != "" {
+		status = append(status, role)
+	}
 
 	if _, err := fmt.Fprintf(w, "%s\t%s\t%s", name, strings.Join(status, ","), translateTimestamp(node.CreationTimestamp)); err != nil {
 		return err
@@ -1520,6 +1524,22 @@ func getNodeExternalIP(node *api.Node) string {
 	return "<none>"
 }
 
+// findNodeRole returns the role of a given node, or "" if none found.
+// The role is determined by looking in order for:
+// * a kubernetes.io/role label
+// * a kubeadm.alpha.kubernetes.io/role label
+// If no role is found, ("", nil) is returned
+func findNodeRole(node *api.Node) string {
+	if role := node.Labels[unversioned.NodeLabelRole]; role != "" {
+		return role
+	}
+	if role := node.Labels[unversioned.NodeLabelKubeadmAlphaRole]; role != "" {
+		return role
+	}
+	// No role found
+	return ""
+}
+
 func printNodeList(list *api.NodeList, w io.Writer, options PrintOptions) error {
 	for _, node := range list.Items {
 		if err := printNode(&node, w, options); err != nil {

pkg/kubectl/resource_printer_test.go

@@ -678,6 +678,36 @@ func TestPrintNodeStatus(t *testing.T) {
 			},
 			status: "Unknown,SchedulingDisabled",
 		},
+		{
+			node: api.Node{
+				ObjectMeta: api.ObjectMeta{
+					Name:   "foo10",
+					Labels: map[string]string{"kubernetes.io/role": "master"},
+				},
+				Status: api.NodeStatus{Conditions: []api.NodeCondition{{Type: api.NodeReady, Status: api.ConditionTrue}}},
+			},
+			status: "Ready,master",
+		},
+		{
+			node: api.Node{
+				ObjectMeta: api.ObjectMeta{
+					Name:   "foo11",
+					Labels: map[string]string{"kubernetes.io/role": "node"},
+				},
+				Status: api.NodeStatus{Conditions: []api.NodeCondition{{Type: api.NodeReady, Status: api.ConditionTrue}}},
+			},
+			status: "Ready,node",
+		},
+		{
+			node: api.Node{
+				ObjectMeta: api.ObjectMeta{
+					Name:   "foo12",
+					Labels: map[string]string{"kubeadm.alpha.kubernetes.io/role": "node"},
+				},
+				Status: api.NodeStatus{Conditions: []api.NodeCondition{{Type: api.NodeReady, Status: api.ConditionTrue}}},
+			},
+			status: "Ready,node",
+		},
 	}
 
 	for _, test := range table {