Ensure VMSS is not under updating before scaling out and only update

caches after async PUT succeeds.

cluster-autoscaler/cloudprovider/azure/azure_scale_set.go

@@ -40,6 +40,7 @@ import (
 	"github.com/Azure/azure-sdk-for-go/services/compute/mgmt/2019-07-01/compute"
 	"github.com/Azure/go-autorest/autorest"
 	"github.com/Azure/go-autorest/autorest/azure"
+	"github.com/Azure/go-autorest/autorest/to"
 )
 
 var (
@@ -261,16 +262,19 @@ 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)
+	}
+
 	// Update the new capacity to cache.
 	vmssSizeMutex.Lock()
 	vmssInfo.Sku.Capacity = &size
@@ -291,6 +295,10 @@ func (scaleSet *ScaleSet) SetScaleSetSize(size int64) error {
 		return rerr.Error()
 	}
 
+	// Proactively set the VMSS size so autoscaler makes better decisions.
+	scaleSet.curSize = size
+	scaleSet.lastSizeRefresh = time.Now()
+
 	klog.V(3).Infof("create a goroutine to wait for the result of the virtualMachineScaleSetsClient.CreateOrUpdate request")
 	go scaleSet.updateVMSSCapacity(future)