XenApp and XenDesktop 7.6 session prelaunch explained

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XenApp and XenDesktop 7.6 session prelaunch explained

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Session prelaunch is one of the set of features created to provide a better user experience working on XenApp and XenDesktop products. XenDesktop session prelaunch was reintroduced in version 7.6 – originally session prelaunch was available in XenApp 6.5 but was removed from the first version of XenDesktop 7.

Introduction 

The session prelaunch help all or specified users access applications quickly, by starting sessions before they are requested. By default session prelaunch is turned off and must be configured manually. In the default configuration each session starts (launches) when a user starts an application, and remains active until the last open application in the session closes. When this option is configured a session is waiting for a user and when the user starts an application prelaunched session is replaced with a regular session. If the user does not start an application (the prelaunched session is unused). We can configure the time when prelaunch session is created and for how long that session remains active. The configuration details are shown in section How to configure ? below.

Key considerations:

The following conditions must be considered when session prelaunch is going to be used:

  • Session prelaunch is configured per Delivery Group
  • The Delivery Group must support applications. If you configure delivery group to deliver only desktops, prelaunch and linger screens will not be available in Edit Delivery Group wizard.
  • Session prelaunch is available only for the machines must be running a VDA for Server OS, minimum version 7.6.
  • Session prelaunch  is supported only when using Citrix Receiver for Windows. In Citrix Receiver 4.2 when you install the Single Sign-on (SSON) component, session prelaunch enabled by default.
  • When using session prelaunch:
    • Physical client machines cannot use the suspend or hibernate power management functions.
    • Client machine users can lock their sessions but should not log off.

Licensing and resource implications

Prelaunched sessions consume a license, but only when connected. Unused prelaunched sessions disconnect after 15 minutes by default. This value can be configured in PowerShell (New/Set-BrokerSessionPreLaunch cmdlet). Optimal configuration balances the benefits of earlier application availability for users against the cost of keeping licenses in use and resources allocated.

Important note: You should carefully verify your licensing model before you enable session prelaunch for all users. This option is fine when you use 1:1 concurrent license or per user/desktop license. If you configure session prelaunch for all users and you have less licenses than total number of workstations you will hit your license limit just in first few minutes in the morning when users will logon to the network (prelaunch session will be created in the background for all users with citrix receiver installed on their computer even though they may not use a XenApp app at all.
If you have other than 1:1 license ratio you can consider to enable session prelaunch only for specified Active Directory groups. You can also try to fix possible problems using short prelaunch timeout - for not used prelaunched sessions or linger timeout to disconnect disconnected sessions but this could be only a workaround.

How to configure ?

To be able to utilize session prelaunch the following configuration task must be completed:

Server side actions:

  1. Configure StoreFront 2.6 for Pass Through Authentication – to configure StoreFront for pass-through authentication follow the steps below:
    1. Open Citrix StoreFront console
    2. In the left pane select Authentication
    3. In the right pane  (Action pane) click Add/Remove Method
    4. Select Domain pass-through and Accept settings
    5. Verify domain pass-through is added and enabled if as it is shown in Figure 1
prel_1

Figure 1

  • Enable and configure Session Prelaunch on XenDesktop 7.6 delivery group – to enable session prelaunch follow the steps below:
    • Open Citrix Studio
    • In the left pane select Delivery Groups
    • In the middle pane select the delivery group you want to modify
    • In the right  pane  (Action pane) click Edit Delivery Group
    • On the left side select Application Prelaunch and configure required settings. You can configure 2 behaviors:
      1. When prelaunch session will be created – Launch when user start an appliaction (no prelaunch) is default selection
      2. How long unused prelaunched sessions remain active – there are two methods to specify how long an unused session remains active when the user does not start an application: a configured timeout and server load thresholds. You can configure all of them; the event that occurs first will cause the unused session to end.
  • Timeout – a configured timeout specifies the number of minutes, hours, or days an unused prelaunched session remains active. If you configure too short a timeout, prelaunched sessions will end before they provide the user benefit of quicker application access. If you configure too long a timeout, incoming user connections might be denied because the server doesn’t have enough resources.You cannot disable this timeout from Studio, but you can in the SDK (New/Set-BrokerSessionPreLaunch cmdlet). If you disable the timeout, it will not appear in the Studio display for that Delivery Group or in the Edit Delivery Group wizard.

    Thresholds – automatically ending prelaunched sessions based on server load ensures that sessions remain open as long as possible, assuming server resources are available. Unused prelaunched sessions will not cause denied connections because they will be ended automatically when resources are needed for new user sessions.You can configure two thresholds: the average percentage load of all servers in the Delivery Group, and the maximum percentage load of a single server in the Delivery Group. When a threshold is exceeded, the sessions that have been in the prelaunch or lingering state for the longest time are ended, sessions are ended one-by-one at minute intervals until the load falls below the threshold. (While the threshold is exceeded, no new prelaunch sessions are started.)

    The example is shown in Figure 2 below

    prel_2

    Figure 2

    1. Configure pass-through settings on client device  – in most cases this will be done via Group Policy. To configure this follow the steps below:
      1. Open Group Policy Editor
      2. Create a new group policy and switch to edit mode
      3. Browse to Computer Configuration -> Administrative Templates
      4. Right click and select Add/Remove templates
      5. Add dd the icaclient.adm this is located in the install location of Receiver “C:\Program Files\Citrix\ICA Client\Configuration”.
      6. Browse to Computer Configuration -> Administrative Templates -> Classic Administrative Templates -> User Authentication -> Local Username and Password
      7. Enable Local user name and password and configure it as it is shown in the Figure 3 below
      8. Link created group policy object to OU with client computersprelunch_5

    Client side actions:

    1. Install citrix receiver with Single Sign on – from the command line use Citrix Receiver with the /includeSSON flag.
    2. Verify if the following registry key is enabled and set to true: HKLM\Software\Citrix\Dazzle\EnablePreLaunch. Based on the citrix blog article, starting from Citrix Receiver 4.2 session prelaunch should be enabled by default. If not enabled, use GPO or other method to enable and configure this registry setting.
    3. Restart client computer

    How to verify if session prelaunch is working  ?

    In order to verify if session prelaunch is configured select the delivery group in Citrix Studio. The result is shown in the figure 4.

    prel_4

    Figure 4

    To display all session lingering settings powershell cmdlet Get-BrokerSessionPreLaunch can be used. The result is displayed in Figure 5.

    prel_7

    Figure 5

    In order to verify if session prelaunch is realy working is to use powershell cmdlet to display all sessions. Use powershell cmdlet get-brokersession to display all sessions with all details as it is shown in Figure 6. Not easy to read for 100 and more sessions 🙂

    prel_5

    Figure 6

     

    I would prefer to add some additional parameters to make the result more readable. Use the following command to display session information in more friendly layout:

    Get-BrokerSession -SessionType Application -Property AppState, SessionState, Uid, UserName, ApplicationsInUse, DnsName, ReceiverName |Format-Table

    The result is shown in Figure 7

    prel_6

    Figure 7

     

     

     

    By | 2016-12-18T19:21:31+00:00 December 5th, 2014|XenApp, XenDesktop|3 Comments

    About the Author:

    I’m a Citrix Architect with 17 years experience in Microsoft and Citrix infrastructure. I have been working with Citrix since Metaframe 1.8 and my primary focus is on Server, Desktop and Application virtualisation with a preference for Citrix products. I’m an enthusiast of Citrix XenDesktop and Provisioning Server.

    3 Comments

    1. John Smith March 24, 2015 at 3:09 pm - Reply

      Hi Andrzej, quick question for you. Have you ever worked with any Citrix products before?

    2. Milind September 2, 2016 at 10:39 am - Reply

      Hi Andrzej,

      Thanks for posting a blog, it help me to know all about session prelaunch. good explained.

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