Use PATCHs instead of PUTs in CIDR allocator

pkg/controller/node/ipam/cloud_cidr_allocator.go

@@ -201,7 +201,6 @@ func (ca *cloudCIDRAllocator) updateCIDRAllocation(nodeName string) error {
 	podCIDR := cidr.String()
 
 	for rep := 0; rep < cidrUpdateRetries; rep++ {
-		// TODO: change it to using PATCH instead of full Node updates.
 		node, err = ca.nodeLister.Get(nodeName)
 		if err != nil {
 			glog.Errorf("Failed while getting node %v to retry updating Node.Spec.PodCIDR: %v", nodeName, err)
@@ -220,8 +219,7 @@ func (ca *cloudCIDRAllocator) updateCIDRAllocation(nodeName string) error {
 			//
 			// See https://github.com/kubernetes/kubernetes/pull/42147#discussion_r103357248
 		}
-		node.Spec.PodCIDR = podCIDR
-		if _, err = ca.client.CoreV1().Nodes().Update(node); err == nil {
+		if err = nodeutil.PatchNodeCIDR(ca.client, types.NodeName(node.Name), podCIDR); err == nil {
 			glog.Infof("Set node %v PodCIDR to %v", node.Name, podCIDR)
 			break
 		}

pkg/controller/node/ipam/range_allocator.go

@@ -25,6 +25,7 @@ import (
 
 	"k8s.io/api/core/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/types"
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/apimachinery/pkg/util/sets"
 	informers "k8s.io/client-go/informers/core/v1"
@@ -37,6 +38,7 @@ import (
 	"k8s.io/kubernetes/pkg/controller"
 	"k8s.io/kubernetes/pkg/controller/node/ipam/cidrset"
 	"k8s.io/kubernetes/pkg/controller/node/util"
+	nodeutil "k8s.io/kubernetes/pkg/util/node"
 )
 
 type rangeAllocator struct {
@@ -282,7 +284,6 @@ func (r *rangeAllocator) updateCIDRAllocation(data nodeAndCIDR) error {
 
 	podCIDR := data.cidr.String()
 	for rep := 0; rep < cidrUpdateRetries; rep++ {
-		// TODO: change it to using PATCH instead of full Node updates.
 		node, err = r.nodeLister.Get(data.nodeName)
 		if err != nil {
 			glog.Errorf("Failed while getting node %v to retry updating Node.Spec.PodCIDR: %v", data.nodeName, err)
@@ -299,8 +300,7 @@ func (r *rangeAllocator) updateCIDRAllocation(data nodeAndCIDR) error {
 			}
 			return nil
 		}
-		node.Spec.PodCIDR = podCIDR
-		if _, err = r.client.CoreV1().Nodes().Update(node); err == nil {
+		if err = nodeutil.PatchNodeCIDR(r.client, types.NodeName(node.Name), podCIDR); err == nil {
 			glog.Infof("Set node %v PodCIDR to %v", node.Name, podCIDR)
 			break
 		}

pkg/controller/node/ipam/range_allocator_test.go

@@ -333,6 +333,7 @@ func TestReleaseCIDRSuccess(t *testing.T) {
 			}(),
 			serviceCIDR:                      nil,
 			subNetMaskSize:                   30,
+			allocatedCIDRs:                   []string{"127.123.234.4/30", "127.123.234.8/30", "127.123.234.12/30"},
 			expectedAllocatedCIDRFirstRound:  "127.123.234.0/30",
 			cidrsToRelease:                   []string{"127.123.234.0/30"},
 			expectedAllocatedCIDRSecondRound: "127.123.234.0/30",

pkg/util/node/node.go

@@ -150,6 +150,21 @@ func SetNodeCondition(c clientset.Interface, node types.NodeName, condition v1.N
 	return err
 }
 
+// PatchNodeCIDR patches the specified node's CIDR to the given value.
+func PatchNodeCIDR(c clientset.Interface, node types.NodeName, cidr string) error {
+	raw, err := json.Marshal(cidr)
+	if err != nil {
+		return fmt.Errorf("failed to json.Marshal CIDR: %v", err)
+	}
+
+	patchBytes := []byte(fmt.Sprintf(`{"spec":{"podCIDR":%s}}`, raw))
+
+	if _, err := c.CoreV1().Nodes().Patch(string(node), types.StrategicMergePatchType, patchBytes); err != nil {
+		return fmt.Errorf("failed to patch node CIDR: %v", err)
+	}
+	return nil
+}
+
 // PatchNodeStatus patches node status.
 func PatchNodeStatus(c v1core.CoreV1Interface, nodeName types.NodeName, oldNode *v1.Node, newNode *v1.Node) (*v1.Node, error) {
 	oldData, err := json.Marshal(oldNode)