Product Documentation

About Smart Scale

Smart Scale enables proactive scaling and power management of registered machines in a XenApp and XenDesktop Site based on a schedule you define or the level of demand for user sessions.

Using Smart Scale you can reduce the costs of running XenApp and XenDesktop in public clouds, such as Microsoft Azure or Amazon Web Services (AWS). Smart Scale does this by dynamically scaling up or scaling down the number of registered powered-on machines in the Delivery Group. Smart Scale can also estimate your savings based on the per-machine costs and utilization history.

Smart Scale manages machine power and capacity using the following methods:

  • Schedule-based scaling: Powers machines on and off based on a schedule you define.
  • Load-based scaling: Powers machines on and off based on the level of demand for sessions.
  • Load and schedule-based scaling: Keeps a minimum number of machines powered on at time periods you define while accommodating the current level of demand for sessions.

For more information about each scaling option, see Manage Delivery Group capacity with Smart Scale.

Capacity and machine registration

To ensure Smart Scale has an accurate view of machines that can accept session requests, Smart Scale includes only machines that are registered with the Site when determining the capacity for a given Delivery Group. Powered-on machines that are unregistered cannot accept session requests, so they are not included in the overall capacity of the Delivery Group.

Scaling across multiple Machine Catalogs

In some XenApp and XenDesktop Sites, multiple Machine Catalogs might be associated with a single Delivery Group to provide high availability across multiple locations. To balance the number of powered on machines in the Delivery Group across all Machine Catalogs, Smart Scale powers on some machines from each associated catalog to meet schedule or session demand requirements. This prevents scaling actions from concentrating in any particular Machine Catalog.

For example, a Delivery Group has two Machine Catalogs: Catalog A has three machines powered on and Catalog B has one machine powered on. If Smart Scale needs to power on five additional machines, it powers on two in Catalog A (totaling five machines on) and three in Catalog B (totaling four machines on).

When machines need to be powered off (because session demand lessens or the schedule requires fewer machines than are powered on), Smart Scale puts the machines in each catalog with the fewest sessions into maintenance mode. While in maintenance mode, Smart Scale waits for remaining sessions to disconnect and terminate (according to Citrix load management policies) before powering off the machines.

Machine provisioning and session demand

Smart Scale works only with the existing machines in a Delivery Group. So, the Machine Catalog associated with the Delivery Group must have enough machines to power on and off as demand increases and decreases. If session demand exceeds the total number of registered machines in the Delivery Group, Smart Scale only ensures all existing registered machines are powered on or taken out of maintenance mode. Smart Tools does not provision more machines.

About the Site Agent

The Smart Tools Site Agent is a lightweight software package that includes the Smart Tools Agent and additional scripts that collect Site information and coordinate power management activities. Once installed on a Delivery Controller in your Site, the Site Agent registers your Site with Smart Tools, detects the Delivery Groups that are configured, and begins monitoring the Site.

For more information about the Site Agent, see Smart Tools Site Agent.

Installing the Site Agent is required if:

  • You deployed your Site without using Smart Tools blueprints and the Site does not already have the Site Agent installed.
  • You deployed your Site with a Smart Tools blueprint that does not automatically install the Site Agent on Delivery Controllers during blueprint deployment. This includes the XenApp and XenDesktop with SQL blueprint, the XenApp and XenDesktop without SQL blueprint, and any custom blueprints that do not include the Register Site built-in step.

Installing the Site Agent is not required if you are using the XenApp and XenDesktop Service for your Site. Smart Tools automatically discovers your Site and coordinates scaling actions directly through the XenApp and XenDesktop Service.

Supported Sites and Delivery Groups

You can use Smart Scale with the following XenApp and XenDesktop Sites:

  • XenApp and XenDesktop 7.x Sites
  • Sites using the XenApp and XenDesktop Service of Citrix Cloud

Supported Sites can use the following host connection types with Smart Scale:

  • Amazon EC2
  • Microsoft Azure (Classic and Resource Manager)
  • Citrix XenServer 6.2, 6.5, 7.0

Smart Scale is configured on a per-Delivery Group basis. You can use Smart Scale with Delivery Groups that reference only Machine Catalogs containing power-managed machines. These machines can be Server OS machines or Desktop OS machines.

Server VDA and VDI support

Smart Scale supports Server OS machines that deliver published applications or hosted shared desktops to users.

VDI desktop support

Smart Scale supports Desktop OS machines hosting the following VDI desktops:

  • Static persistent (dedicated) VDI desktops
  • Random non-persistent VDI desktops (pooled VDI desktops)

To use Smart Scale with VDI desktop machines, you must disable XenApp and XenDesktop’s built-in power management functions so they don’t interfere with Smart Scale’s scaling actions.

Important: The commands in this section disable XenDesktop’s built-in power management functions for all Delivery Groups in the Site. This action cannot be undone automatically. Citrix recommends using these commands in a test environment only. Prior to using these commands, consider recording the current Delivery Group settings that the commands will alter when executed.

To do this for a traditional Site, from the Delivery Controller, open the PowerShell command window and enter the following commands:

Add-PSSnapin *Citrix*
Set-BrokerDesktopGroup -Name * -AutomaticPowerOnForAssigned $False
Set-BrokerDesktopGroup -Name * -AutomaticPowerOnForAssignedDuringPeak $False
Set-BrokerDesktopGroup -Name * -OffPeakBufferSizePercent 0
Set-BrokerDesktopGroup -Name * -PeakBufferSizePercent 0
Set-BrokerPowerTimeScheme -name * -PoolSize ( 1..24 | %{ -1 } ) -PoolUsingPercentage 0

For Sites that use XenDesktop Essentials or the XenApp and XenDesktop Service, perform the following actions:

  1. Download the XenApp and XenDesktop Remote PowerShell SDK and run it on a machine in your resource location. Citrix recommends running this SDK on machines that do not act as Cloud Connectors in your resource location.
  2. Open a PowerShell command window and run the commands mentioned above.

Supported scaling options

Depending on the Machine Catalogs associated with your Delivery Groups, some scaling options might not be available. The table below shows the Machine Catalogs that are supported for each scaling option.

Machine Type Schedule-based Load-based Load and schedule-based
Server OS machines hosting published applications or hosted shared desktops (Server VDI) Supported. Supported. Supported.
Desktop OS machines hosting static persistent (dedicated) VDI desktops Supported. During periods when machines are powered off (for example, after working hours), users can trigger machines to power on through Citrix Receiver. You can set Smart Scale’s Power Off Delay so Smart Scale does not automatically power machines off before the user can establish a session. Not currently supported. Not currently supported.
Desktop OS **machines hosting **random non-persistent VDI desktops (pooled VDI desktops) Supported. Supported. Use the Session Count scaling metric and set the maximum number of sessions to 1. Supported. Use the Session Count scaling metric and set the minimum number of machines to 1.

Supported scalability

Smart Scale supports power managing Sites using XenApp and XenDesktop, the XenApp and XenDesktop Service, XenApp Essentials, and XenDesktop Essentials.

Power management for a single Site using one of these services is supported as follows:

  • Up to 2,000 VDAs or VDIs per Site can be power managed.
  • Up to 120 Delivery Groups can be power managed.
  • Up to 1,000 VDAs or VDIs per Delivery Group can be power managed.

Important: If you add a Site to Smart Scale that exceeds these limits, you might not be able to use Smart Scale with your Site. When you add your Site to Smart Scale, Smart Tools verifies the Delivery Groups and machines in the Site are within the supported limit. If the Site exceeds the limit, Smart Scale does not enable the “Get Started” button, preventing you from configuring Smart Scale for the Site. If you need to add a Site that exceeds these limits, contact Citrix Technical Support.

Availability of monitoring data

For all supported Sites, monitoring and event data are available when Smart Scale is enabled for the Delivery Group. Monitoring data continues to be available when Smart Scale is enabled and then disabled for the Delivery Group. Smart Scale collects monitoring data at 5 minute intervals.

Note: When you initially add a Site to Smart Scale, it might take a few minutes to display monitoring data for your Site.

Service notifications

Smart Tools outage and maintenance events are listed on the Citrix Cloud Service Health Dashboard at This page displays service status and incidents in real-time for all Citrix Cloud services.

You can subscribe to status notifications for Smart Tools through email, SMS, Slack, or other webhook. For instructions, see the “Service notifications” section in About Citrix Cloud and Citrix Smart Tools.