Fix panic for GetZoneByNodeName on Azure Stack (#8755)

* Fix panic for GetZoneByNodeName on Azure Stack

Azure Stack does not support the API Version, 2020-12-01, for
PlatformFaultDomain, and therefore panics when we run the cloud
provider on Azure Stack. This avoids the panic, but we cannot
get the correct PlatformFaultDomain (which may not be an issue).

* Add GetZoneByNodeName test for VM with no zones

Author: patrickdillon

pkg/provider/azure_standard.go

@@ -580,7 +580,11 @@ func (as *availabilitySet) GetZoneByNodeName(ctx context.Context, name string) (
 		failureDomain = as.makeZone(ptr.Deref(vm.Location, ""), zoneID)
 	} else {
 		// Availability zone is not used for the node, falling back to fault domain.
-		failureDomain = strconv.Itoa(int(ptr.Deref(vm.Properties.InstanceView.PlatformFaultDomain, 0)))
+		if prop := vm.Properties; prop == nil || prop.InstanceView == nil {
+			failureDomain = "0"
+		} else {
+			failureDomain = strconv.Itoa(int(ptr.Deref(vm.Properties.InstanceView.PlatformFaultDomain, 0)))
+		}
 	}
 
 	zone := cloudprovider.Zone{

pkg/provider/azure_standard_test.go

@@ -1192,6 +1192,22 @@ func TestGetStandardVMZoneByNodeName(t *testing.T) {
 			},
 			expectedErrMsg: fmt.Errorf("failed to parse zone %q: strconv.Atoi: parsing %q: invalid syntax", []string{"a"}, "a"),
 		},
+		{
+			name:     "GetZoneByNodeName should set failuredomain to 0 if no zones are found",
+			nodeName: "vm5",
+			vm: &armcompute.VirtualMachine{
+				Name:     ptr.To("vm5"),
+				Location: ptr.To("HybridEnvironment"),
+				Zones:    []*string{},
+				Properties: &armcompute.VirtualMachineProperties{
+					InstanceView: nil, // can be nil on Azure Stack
+				},
+			},
+			expectedZone: cloudprovider.Zone{
+				FailureDomain: "0",
+				Region:        "hybridenvironment",
+			},
+		},
 	}
 	for _, test := range testcases {
 		mockVMClient := cloud.ComputeClientFactory.GetVirtualMachineClient().(*mock_virtualmachineclient.MockInterface)