Merge pull request #58186 from negz/master

Automatic merge from submit-queue (batch tested with PRs 57266, 58187, 58186, 46245, 56509). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Avoid panic in Cloud CIDR Allocator

**What this PR does / why we need it**:
I suspect a race exists where we attempt to look up the CIDR for a terminating node. By the time `updateCIDRAllocation` is called the node has disappeared. We determine it does not have a cloud CIDR (i.e. Alias IP Range) and attempt to record a `CIDRNotAvailable` node status. Unfortunately we reference `node.Name` while `node` is still nil.

By getting the node before looking up the cloud CIDR we avoid the nil pointer dereference, and potentially fail fast in the case the node has disappeared.

**Which issue(s) this PR fixes**:
Fixes #58181

**Release note**:

```release-note
Avoid panic when failing to allocate a Cloud CIDR (aka GCE Alias IP Range). 
```

pkg/controller/nodeipam/ipam/cloud_cidr_allocator.go

@@ -191,10 +191,14 @@ func (ca *cloudCIDRAllocator) AllocateOrOccupyCIDR(node *v1.Node) error {
 
 // updateCIDRAllocation assigns CIDR to Node and sends an update to the API server.
 func (ca *cloudCIDRAllocator) updateCIDRAllocation(nodeName string) error {
-	var err error
-	var node *v1.Node
 	defer ca.removeNodeFromProcessing(nodeName)
 
+	node, err := ca.nodeLister.Get(nodeName)
+	if err != nil {
+		glog.Errorf("Failed while getting node %v for updating Node.Spec.PodCIDR: %v", nodeName, err)
+		return err
+	}
+
 	cidrs, err := ca.cloud.AliasRanges(types.NodeName(nodeName))
 	if err != nil {
 		nodeutil.RecordNodeStatusChange(ca.recorder, node, "CIDRNotAvailable")
@@ -210,12 +214,6 @@ func (ca *cloudCIDRAllocator) updateCIDRAllocation(nodeName string) error {
 	}
 	podCIDR := cidr.String()
 
-	node, err = ca.nodeLister.Get(nodeName)
-	if err != nil {
-		glog.Errorf("Failed while getting node %v for updating Node.Spec.PodCIDR: %v", nodeName, err)
-		return err
-	}
-
 	if node.Spec.PodCIDR == podCIDR {
 		glog.V(4).Infof("Node %v already has allocated CIDR %v. It matches the proposed one.", node.Name, podCIDR)
 		// We don't return here, in order to set the NetworkUnavailable condition later below.