Ensure VMSS is not under updating before scaling out

cluster-autoscaler/cloudprovider/azure/azure_fakes.go

@@ -80,7 +80,7 @@ func (client *VirtualMachineScaleSetsClientMock) CreateOrUpdateAsync(ctx context
 
 // WaitForAsyncOperationResult waits for the response of the request
 func (client *VirtualMachineScaleSetsClientMock) WaitForAsyncOperationResult(ctx context.Context, future *azure.Future) (*http.Response, error) {
-	return nil, nil
+	return &http.Response{StatusCode: http.StatusOK}, nil
 }
 
 // DeleteInstances deletes a set of instances for specified VirtualMachineScaleSet.

cluster-autoscaler/cloudprovider/azure/azure_scale_set.go

@@ -40,6 +40,7 @@ import (
 	"github.com/Azure/azure-sdk-for-go/services/compute/mgmt/2019-12-01/compute"
 	"github.com/Azure/go-autorest/autorest"
 	"github.com/Azure/go-autorest/autorest/azure"
+	"github.com/Azure/go-autorest/autorest/to"
 )
 
 var (
@@ -253,7 +254,7 @@ func (scaleSet *ScaleSet) updateVMSSCapacity(future *azure.Future) {
 		return
 	}
 
-	klog.Errorf("virtualMachineScaleSetsClient.WaitForCreateOrUpdate for scale set %q failed: %v", scaleSet.Name, err)
+	klog.Errorf("virtualMachineScaleSetsClient.WaitForAsyncOperationResult for scale set %q failed: %v", scaleSet.Name, err)
 }
 
 // SetScaleSetSize sets ScaleSet size.
@@ -261,19 +262,27 @@ func (scaleSet *ScaleSet) SetScaleSetSize(size int64) error {
 	scaleSet.sizeMutex.Lock()
 	defer scaleSet.sizeMutex.Unlock()
 
-	// Proactively set the VMSS size so autoscaler makes better decisions.
-	scaleSet.curSize = size
-	scaleSet.lastSizeRefresh = time.Now()
-
 	vmssInfo, rerr := scaleSet.getVMSSInfo()
 	if rerr != nil {
 		klog.Errorf("Failed to get information for VMSS (%q): %v", scaleSet.Name, rerr)
 		return rerr.Error()
 	}
 
+	// Abort scaling to avoid concurrent VMSS scaling if the VMSS is still under updating.
+	// Note that the VMSS provisioning state would be updated per scaleSet.sizeRefreshPeriod.
+	if vmssInfo.VirtualMachineScaleSetProperties != nil && strings.EqualFold(to.String(vmssInfo.VirtualMachineScaleSetProperties.ProvisioningState), string(compute.ProvisioningStateUpdating)) {
+		klog.Errorf("VMSS %q is still under updating, waiting for it finishes before scaling", scaleSet.Name)
+		return fmt.Errorf("VMSS %q is still under updating", scaleSet.Name)
+	}
+
+	// Proactively set the VMSS size so autoscaler makes better decisions.
+	scaleSet.curSize = size
+	scaleSet.lastSizeRefresh = time.Now()
+
 	// Update the new capacity to cache.
 	vmssSizeMutex.Lock()
 	vmssInfo.Sku.Capacity = &size
+	vmssInfo.VirtualMachineScaleSetProperties.ProvisioningState = to.StringPtr(string(compute.ProvisioningStateUpdating))
 	vmssSizeMutex.Unlock()
 
 	// Compose a new VMSS for updating.

cluster-autoscaler/cloudprovider/azure/azure_scale_set_test.go

@@ -20,9 +20,11 @@ import (
 	"fmt"
 	"net/http"
 	"testing"
+	"time"
 
 	"github.com/Azure/azure-sdk-for-go/services/compute/mgmt/2019-12-01/compute"
 	"github.com/Azure/go-autorest/autorest"
+	"github.com/Azure/go-autorest/autorest/to"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/mock"
 
@@ -97,6 +99,60 @@ func TestIncreaseSize(t *testing.T) {
 	assert.Equal(t, 5, targetSize)
 }
 
+func TestIncreaseSizeOnVMSSUpdating(t *testing.T) {
+	manager := newTestAzureManager(t)
+	vmssName := "vmss-updating"
+	var vmssCapacity int64 = 3
+	scaleSetClient := &VirtualMachineScaleSetsClientMock{
+		FakeStore: map[string]map[string]compute.VirtualMachineScaleSet{
+			"test": {
+				vmssName: {
+					Name: &vmssName,
+					Sku: &compute.Sku{
+						Capacity: &vmssCapacity,
+					},
+					VirtualMachineScaleSetProperties: &compute.VirtualMachineScaleSetProperties{
+						ProvisioningState: to.StringPtr(string(compute.ProvisioningStateUpdating)),
+					},
+				},
+			},
+		},
+	}
+	manager.azClient.virtualMachineScaleSetsClient = scaleSetClient
+	registered := manager.RegisterAsg(newTestScaleSet(manager, vmssName))
+	assert.True(t, registered)
+	manager.regenerateCache()
+
+	provider, err := BuildAzureCloudProvider(manager, nil)
+	assert.NoError(t, err)
+
+	// Scaling should fail because VMSS is still under updating.
+	scaleSet, ok := provider.NodeGroups()[0].(*ScaleSet)
+	assert.True(t, ok)
+	err = scaleSet.IncreaseSize(1)
+	assert.Equal(t, fmt.Errorf("VMSS %q is still under updating", scaleSet.Name), err)
+
+	// Scaling should succeed after VMSS ProvisioningState changed to succeeded.
+	scaleSetClient.FakeStore = map[string]map[string]compute.VirtualMachineScaleSet{
+		"test": {
+			vmssName: {
+				Name: &vmssName,
+				Sku: &compute.Sku{
+					Capacity: &vmssCapacity,
+				},
+				VirtualMachineScaleSetProperties: &compute.VirtualMachineScaleSetProperties{
+					ProvisioningState: to.StringPtr(string(compute.ProvisioningStateSucceeded)),
+				},
+			},
+		},
+	}
+	scaleSetStatusCache.mutex.Lock()
+	scaleSetStatusCache.lastRefresh = time.Now().Add(-1 * scaleSet.sizeRefreshPeriod)
+	scaleSetStatusCache.mutex.Unlock()
+	err = scaleSet.IncreaseSize(1)
+	assert.NoError(t, err)
+}
+
 func TestBelongs(t *testing.T) {
 	provider := newTestProvider(t)
 	registered := provider.azureManager.RegisterAsg(