code: public ServiceFuture<VirtualMachineScaleSetExtensionInner> createOrUpdateAsync(String resourceGroupName, String vmScaleSetName, String vmssExtensionName, VirtualMachineScaleSetExtensionInner extensionParameters, final ServiceCallback<VirtualMachineScaleSetExtensionInner> serviceCallback) {
          return ServiceFuture.fromResponse(createOrUpdateWithServiceResponseAsync(resourceGroupName, vmScaleSetName, vmssExtensionName, extensionParameters), serviceCallback);
      }
docs: The operation to create or update an extension.
  
  @param resourceGroupName The name of the resource group.
  @param vmScaleSetName The name of the VM scale set where the extension should be create or updated.
  @param vmssExtensionName The name of the VM scale set extension.
  @param extensionParameters Parameters supplied to the Create VM scale set Extension operation.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object