Manage Delivery Group capacity with Smart Scale

Contents

Enable or disable Smart Scale for a Delivery Group

  1. From the menu bar, click Smart Scale.
  2. On the Smart Scale page, locate the Site you want to manage and click View details
  3. On the Site's details page, click Configure
  4. On the Smart Scale configuration page, select the Delivery Group you want to manage.
  5. To enable Smart Scale, click the Smart Scale Disabled toggle button. The toggle button turns green to indicate Smart Scale is enabled for the selected Delivery Group. 
  6. To disable Smart Scale, click the Smart Scale Enabled toggle button. The toggle button turns grey to indicate Smart Scale is disabled for the selected Delivery Group.

Important: XenApp and XenDesktop's native power management functions for VDI desktops might interfere with Smart Scale's scaling activities. If your Site has these power management actions already configured, you must disable them when using Smart Scale.

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Scale machines based on a schedule

Schedule-based scaling enables you to keep a minimum number of machines, including no (zero) machines, in the Delivery Group powered on at certain times of day that you define. The schedule is based on the time zone of the Delivery Group. By default, Smart Tools keeps a single machine powered on during intervals when no other schedule is defined. 

When you define a schedule and specify a minimum number of machines, Smart Tools powers on or off machines to meet the minimum you specify. If the schedule period requires more machines than are currently powered on, Smart Tools powers on additional machines to meet the minimum number specified. If there are any powered-on machines currently in maintenance mode, Smart Tools takes them out of maintenance mode before powering on more machines.

If the schedule period requires fewer machines than are currently powered on, Smart Tools puts the excess machines with the fewest sessions into maintenance mode. During maintenance mode, Citrix policies take effect to disconnect and terminate any remaining sessions. When all sessions have been terminated, Smart Tools powers off the machine. 

Citrix policies for terminating sessions

To ensure disconnected and idle sessions are terminated appropriately, configure the following Citrix policies for your Site:

  • Disconnected session timer
  • Disconnected session timer interval
  • Session idle timer
  • Session idle timer interval

For more information about these policy settings, see Session limits policy settings on the Citrix Product Documentation web site.

Considerations

  • If you define multiple schedules for a Delivery Group, ensure the schedules begin and end sequentially. For example, Schedule A is 8 AM-5 PM weekdays; Schedule B is 5 PM-12 AM weekdays; and so on. Smart Scale does not support overlapping schedules defined for the same Delivery Group. 
  • Ensure the Minimum # of Machines On value is smaller than the total number of machines in the Delivery Group. If this value is larger than the total number, Smart Tools powers on all the machines in the Delivery Group. Smart Tools does not provision additional machines to the Machine Catalog associated with the Delivery Group. 

To enable schedule-based scaling

  1. On the Smart Scale configuration page, select the Delivery Group you want to manage. 
  2. Under Capacity Management, select Schedule-based scaling only
  3. Click Create New. The Create Schedule box appears.
  4. In Name, enter a name for the schedule item.
  5. In Min # of Machines On, enter the minimum number of machines that should be powered on during the schedule period. If you don't want any machines on during the period, enter 0 (zero).
  6. Enter the starting and ending times when the machines should remain powered on. Additionally, select one of the following durations:
    • All Workweek days: Keeps machines powered on for a 5-day work week (Monday through Friday).
    • All Weekend days: Keeps machines powered on for a 2-day weekend (Saturday and Sunday).
    • Entire week: Keeps machines powered on for a 7-day period (Sunday through Saturday).
    • Custom: Keeps machines powered on for the days you select. 
  7. Click Create
  8. Click Done to save the configuration.

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Scale machines based on load and schedule

Load-based scaling ensures a sufficient number of machines are powered on to meet the demand for user sessions at any given time. Load-based and schedule-based scaling enables you to keep a minimum number of machines powered on during certain times of day that you define and to accommodate increases or decreases in demand during those times. As with schedule-based only scaling, the schedule is based on the time zone of the Delivery Group.

To use load-based scaling (with or without schedules), you need to specify the scale metric you want to use for determining when machines are at full load and triggering scaling actions.

Scale metrics

Smart Tools uses the scale metric you select to direct users to the machine best suited to host the sessions they request. When you select a scale metric, you will also need to configure the Load per machine setting which establishes the level at which Smart Tools considers a machine at full load.

Session count 

The Session count metric enables you to set a maximum number of sessions that are allowed on each machine in the Delivery Group. When the maximum number of sessions is reached, Smart Tools directs new session requests to other machines in the Delivery Group.

When you select this metric, you also specify the maximum number of sessions each machine in your Delivery Group can support. Smart Tools uses this value to calculate the capacity of powered-on machines in the Delivery Group. It does not affect any Citrix load management policy settings that you have configured.

Load index

The Load index metric determines how likely a machine is to receive connections. Load index is calculated using the Citrix Load Management policy settings configured for concurrent logon, session, CPU, disk, and memory use. By default, a machine is considered at full load if there are at least two session requests waiting to be resolved or the machine is hosting 250 sessions.

When you select this metric, Smart Tools uses the value 10000 as the maximum load index by default.

Capacity and scaling

Smart Scale adds a capacity buffer to the current session demand to accommodate any sudden spikes in demand. By default, the capacity buffer is 10% of the current demand. For example, if the current demand is 100 sessions, Smart Scale accounts for 110 sessions. You can modify this buffer, increasing or decreasing it based on your session needs and resource cost considerations.

If session demand exceeds the maximum load that the currently powered-on machines can bear, Smart Tools powers on additional machines to meet the demand. If there are any powered-on machines currently in maintenance mode, Smart Tools takes the machines out of maintenance mode before powering on more machines.

If the session demand decreases, the excess machines with the fewest sessions are put into maintenance mode. During maintenance mode, Citrix policies take effect to disconnect and terminate any remaining sessions. After all sessions have been terminated, Smart Tools powers off the machine. 

For a list of the policies you configure for terminating sessions in your XenApp and XenDesktop Site, see Citrix policies for terminating sessions in this topic.

Considerations for accommodating demand

Smart Scale works with existing machines in the Delivery Group, so you must ensure the Machine Catalog associated with the Delivery Group has sufficient machines available to accommodate increases in session demand. If demand for sessions is greater than the total number of machines can accommodate, Smart Tools powers on all machines in the Delivery Group and records on the Events tab that no more machines are available to power on.

To enable load-based scaling or load and schedule-based scaling

  1. On the Smart Scale configuration page, select the Delivery Group you want to manage.
  2. Under Capacity Management, select Load-based scaling only or Load-based and schedule-based scaling.
  3. In Scale metric, select the metric you want to use for managing load in your Delivery Group. To manage load using number of sessions, select Session count. To manage load using load index, select Load index
  4. In Load per machine, if you use session count for the scale metric, enter the Max number of sessions that each machine in the Delivery Group is allowed to host. Entering a lower value can improve performance for logged on sessions, but powers on more machines when session demand rises. If you use load index for the scale metric, the default maximum load index is 10000.
  5. If applicable, under Schedules, click Create New and enter a name, time period, and duration. Click Create.
  6. To modify the capacity buffer, click Advanced. Adjust the slider to increase or decrease the number of spare sessions that Smart Scale accounts for in addressing sudden demand. Increasing the buffer results in more machines powered on and waiting for session requests. Click OK to save your changes.
  7. Click Done to save the configuration.

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Configure estimated savings for cloud instances

If your Site consists of machines deployed in the cloud, Smart Scale can estimate the amount you save in resource costs based on the per-instance cost and the utilization history of the Site.

  1. On the Smart Scale page, select the Site you want to manage and click View Details. The Site details page appears.
  2. Click Configure. The Smart Scale Configuration page appears.
  3. Under Monitoring, enter the hourly price in US dollars for each instance in your Site. Click Done.

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