When you publish resources in Parallels RAS, you need to specify one or more servers that host them. Host pools allow you to combine multiple RD Session Hosts and then publish the resources from the host pool instead of specifying individual servers.

The main benefits of using RD Session Host host pools are as follows:

• They simplify the management of published resources.

• They allow you to use RD Session Hosts created from a template. More on this later in this section.

Each RD Session Hosts must belong to a host pool. Parallels RAS comes with a built-in host pool named <Default> that you can use. Note that an RD Session Host can be a member of one host pool only. You cannot add the same server to multiple host pools.

Moving an RD Session Host to another host pool

To move an RD Session Host from one host pool to another:

1. In the RAS console, navigate to Farm > <Site> > RD Session Hosts.

2. Select an RD Session Host.

3. Click Tasks > Assign to host pool or right-click the RD Session Host and select Assign to host pool in the context menu.

4. In the Assign to Host pool dialog, select the host pool you need.

Autoscale

The settings on the Autoscale tab of the host pool properties determine how RD Session Hosts are created from the specified template. The settings are described below.

Template: Specifies the template assigned to the host pool.

Enable autoscale: Enables autoscale.

Configure: Configures the autoscale settings:

• Min number of hosts to be added to the host pool from the Template: Specifies the minimum number of servers that will be added to the host pool automatically when the template is assigned to the host pool. This number of servers will remain in the host pool irrespective of utilization.

• Max number of hosts to be added to the host pool from the Template: This option allows you to set a limit on how many servers in total can be added to the host pool from the template. A template can be shared between host pools. By setting a limit for each host pool, you can ensure that the combined number of servers in each host pool will not exceed the template limit. Consider the following examples:

  • If the template is used by a single host pool, then this number can be up to the Maximum hosts setting of the template.

  • If two or more host pools share the same template, then the combined number from all host pools must be less or equal to the Maximum hosts settings of the template.

  When you save a host pool, a validation will be performed against other host pools (if any) and you will see an error message if the numbers don't match. Note that when a server cannot be created on request due to an error, a "Template error" event is triggered and the administrator will receive an alert message.

• Add new or power on existing hosts when workload is above (%): Specifies a workload threshold in percent. When the actual workload is above this value, a new server (or servers) will be created and added to the host pool (if not already available). The host pool workload percentage is calculated using the following formula:

  Host pool Workload = (Current Sessions / Max Sessions) * 100

  In the formula above:

  • Current Sessions is the total number of all sessions on all servers in the host pool. This includes static (standalone) servers and servers created from the template (host pools). Note that servers that are disabled, being drained, or have the agent status of ‘Not Verified’ are not included in the calculation.

  • Max Sessions is a setting that you specify on the Agent Settings tab (either inherited from Site defaults or overridden for this host pool) and the maximum number of sessions allowed for the host pool.

  Consider the following examples:

  RAS Host pool 1 — mixed server types (static and host pools), different agent status:

  • RDSH-1, Status: OK, Max Sessions 10, Current Sessions: 2, Type: Static

  • RDSH-2, Status: Disabled, Max Sessions 20, Current Sessions: 0, Type: Static

  • RDSH-3, Status: OK, Max sessions 10, Current Sessions: 4, Type: Host

  • RDSH-4, Status: Drain Mode, Max sessions 10, Current Sessions: 3, Type: Host

  For the host pool above, the workload is calculated as (Current Sessions / Max Sessions) * 100 or ((2 + 4) / 20) * 100 = 30%

  Note that servers RDSH-2 and RDSH-4 are not included in the workload because the former has the agent disabled and the latter is in drain mode.

  RAS Host pool 2 — mixed server types (static and host pools), different agent status:

  • RDSH-1, Status: OK, Max Sessions 10, Current Sessions: 0, Type: Host

  • RDSH-2, Status: OK, Max Sessions 10, Current Sessions: 2, Type: Host

  • RDSH-3, Status: Not Verified, Max sessions 10, Current Sessions: 0, Type: Host

  Host pool Workload = (Current Sessions / Max Sessions) * 100 or ((0 + 2) / 20) * 100 = 10%

  Please note that a host pool will always make sure that it has at least one server available, even if the workload is zero percent.

• Number of hosts to be added to the host pool per request: Specifies how many servers should be created when the workload goes above the threshold value. This setting works together with the Add servers from template when workload is above (%) setting described above. When a host pool sends a request to the template to create additional servers, the value specified here will determine the number of servers that will be created.

• Drain and power off hosts from host pool when workload is below (%): Specifies a workload threshold in percent. When the actual workload is below this value and remains there for a period specified in the Workload remains below this level field, excessive hosts will be switched to drain mode or powered off. The period of time can be selected from the drop-down list or you can type your own integer value using "weeks", "days", "hours", "minutes", or "seconds" as a unit measure. The server(s) with the least number of sessions will be switched to drain mode. As soon as all users are logged off from a server, it is unassigned from the host pool. At that point, the server becomes available to other host pools on demand.

• Remove hosts from host pool after drain and power off: Specifies if hosts should be removed from the host pool after being drained and powered off.

Tip: Servers are unassigned from the host pool only when all user sessions on that particular server are logged off. In case user sessions are still present, such as user sessions in idle, active or disconnected state, autoscaling does not log off user sessions and does not unassign the server from a host pool.

Using host pool defaults

RD Sessions Hosts assigned to a host pool have various settings that they can inherit from the host pool defaults. This makes it simpler to configure a single set of settings for all servers instead of configuring each server individually. A Site also has its own default settings (Site defaults). Moreover, an RD Session Host host pool can inherit these Site defaults. This gives you the following choices when inheriting default settings by an RD Session Host:

• Configure Site defaults and make the host pool inherit these settings. The RD Session Hosts assigned to the host pool will therefore also inherit Site defaults. This is the default scenario for a new host pool. Site defaults can be configured by navigating to Farm > <Site> > RD Session hosts and clicking Tasks > Site defaults.

• Configure default settings for a given host pool. This way you can have multiple host pools, each having its own host pool defaults (different from Site defaults). Therefore, the servers assigned to a host pool will inherit the host pool's defaults.

To configure default settings for a host pool, open the Host pool Properties dialog (Tasks > Properties), select a desired tab (except the General tab, which doesn't have any defaults) and select or clear the Inherit default settings option. If you clear the option, you can specify your own defaults. All servers that are (or will be) assigned to this host pool will inherit these settings. Note that inheritance works independently for each individual tab on the host pool properties dialog.

For information on how default settings are configured for an RD Session Host, see View and modify RD Session Host properties.

You can enable and configure automatic updates for all RD Session Host Agents in a host pool.

Schedule Agent auto-upgrade

To schedule Agent auto-upgrade:

1. Go to Farm > Site > RD Session Hosts > Host pools > Properties > Auto-upgrade tab.

2. Clear the Inherit default settings options if you want to modify them for this host pool.

3. Select the Enable auto-upgrade maintenance window option. During the maintenance window, all hosts in the host pool will try to download Agent upgrades. The upgrades will be downloaded and installed as soon as all users log out of their hosts. New logons from users are prohibited (drain mode). If the users don't log off during a maintenance window, the upgrades won't be installed until the next window.

4. Specify the start date and time, duration, and recurrence settings for this event. To make this a one-time event, select Never in the Recur drop-down list.

5. (Optional) If you want to forcefully log off all users and download the upgrades at the end of a maintenance window, select the Force logoff of current sessions at the end of the maintenance window duration option.

6. (Optional) Configure a message that will be sent to users before or during a maintenance window. Click the Configure messages button and specify the message title, body, and the time period when it should be sent.

Cancel Agent auto-update

To cancel Agent auto-update:

1. Go to Farm > Site > RD Session Hosts > Host pools.

2. Select Tasks > Cancel auto-upgrade maintenance window.

Read this section to learn how manage RD Session Hosts components in Parallels RAS.

Creating a host pool

To create an RD Session Host host pool:

1. In the RAS console, navigate to Farm > <Site> > RD Session HostsHost pools.

2. Click Tasks > Add (or click the [+] icon).

3. Select Enable Host pool in site to enable the host pool. Specify the name and the description for the new host pool.

4. Click Next.

5. On the Provisioning page, select whether this host pool will contain template-based or standalone hosts:

   • Standalone: (Template-based and standalone RD Session Hosts) Select one or more hosts that already exist. You'll be able to do it in the next step or you can do it later. Prior to adding hosts to host pools, ensure that hosts are domain joined and have network access to the domain environment. Note that the Standalone provisioning is considered "unmanaged" as it lacks some of the functionality, such as Autoscaling.

6. Click Next.

7. Depending on the selection made on the Provisioning page (above), do one of the following

   • Standalone: Select one or more hosts from the list to be included in the host pool (you can also add hosts to the pool later).

   • Template: Select a template from the list or click Create new to create a new template and specify the template settings. Versions: If you selected an existing template, select one of its versions. Enable autoscale: (Multi-session hosts) Enable and configure autoscale.

8. Click Next.

9. (Templates only) On the General page, specify the following options:

   • Template name: Choose and type a template name.

   • Maximum hosts: Specify the maximum number of hosts that can be created from this template.

   • Number of hosts deployed on wizard completion: The number of hosts to deploy once the template is created. Please keep in mind that this will take some time because the hosts will be created one at a time.

   • Host name: A pattern to use when naming new hosts.

10. Click Next.

11. (Templates only) On the Additional properties page, specify the following options:

    • Keep available buffer: The minimum number of hosts to always keep unassigned and session free for the template. As soon as the number of free and unassigned desktops drops below the setting value, it forces the template to create another host. The template uses its own settings for host creation including initial power state.

    • Host state after the preparation: Select the power state that should be applied to a host after it is prepared. Choose from Powered on, Powered off, or Suspended. Note that when the power state is set to Power off or Suspended, the number of running (fully ready and waiting for incoming connections) hosts is controlled by the Keep available buffer setting (see above). For example, let's say the Maximum hosts value is set at 200, the number of guest hosts deployed on wizard completion is 100, and the power state after preparation is Powered off. The result of such a configuration will be 100 clones deployed and powered off.

    • Delete unused hosts after: Select what to do with unused hosts to save resources. Choose whether to never delete them or specify the time period after which they should be deleted.

12. Click Next.

14. Click Next.

15. On the Summary page, review the template summary information. You can click the Back button to correct some of the information if needed.

16. Finally, click Finish to create the host pool and close the wizard.

When you create RD Session Host host pools, you can assign a template to a host pool. This can be done when you create or modify a host pool, or it can be done from the Templates tab.

To assign a template to a host pool:

1. Go to Farm > Site > RD Session Hosts > Templates tab.

2. On the Templates tab, select a template.

3. Click Tasks > Assign to host pool.

4. Select the template version in the Version dialog.

5. A dialog opens listing existing RD Session Host host pools. Host pools that already have a template assigned are not shown in this list by default. To display them, select the Show host pools with assigned template option. The template that they are currently using is displayed in the Template column.

6. Select one or more host pools and click OK.

To remove a template from a host pool or host pool:

1. Select a template and click Tasks > Remove from host pool.

2. A dialog opens listing all host pools to which this template is assigned.

3. Select the host pools to remove the template from and click OK.

Note that if a host pool has hosts created from the template that you are removing, they will be removed as well. A message is displayed where you need to confirm the removal.

RD Session Host templates are designed specifically to give you the ability to replicate RD Session Hosts running in virtual machines. Hosts created from an RD Session Host template are treated by Parallels RAS almost like regular RD Session Hosts. The main difference is, you can create as many hosts from a single template as you require, thus automating RD Session Host provisioning according to your needs.

RD Session Host templates are supported on the following VDI platforms:

• Microsoft Hyper-V

• Microsoft Hyper-V Failover Cluster

• VMware VCenter

• VMware ESXi

• SC//HyperCore

• Nutanix AHV (AOS)

• Microsoft Azure

• Amazon Web Services

RD Session Host templates support Windows Server 2008 R2 up to Windows Server 2022 as a guest OS. Compared to regular RD Session Hosts, servers created from an RD Session Host template do not support earlier versions of Windows Server. The reason is, these servers run in VMs and require the RAS Guest Agent installed in them, so the guest OS requirements are limited by Windows Server versions supported by RAS Guest Agent.

Please note that the following standard RAS VDI features are not available when using RD Session Host templates:

• Pool management

• Persistent hosts

• Session management

• Publishing from a specific Template

• Some other strictly RAS VDI specific features.

For the information on how to provision RD Session Hosts created from a template, see Manage host pools (RD Session Hosts).

Requirements

To complete the tasks described in this section, the following requirements must be met:

• Requirements described in the "Requirements" subsection of Creating a VM template.

• Network Discovery UDP port 137 must be enabled for a domain firewall profile in the guest OS. This can be done via domain group policies or manually in the guest OS.

Manual agent installation

Normally, you will push install the necessary agent software in a source VM right from the Parallels RAS console. However, you can also install the software manually by running the Parallels RAS installer in Windows in the VM. When doing so, use the Custom installation option and select the following agent components RAS Guest Agent and RAS RD Session Host Agent to be installed in the source VM.

Create a template

To create an RD Session Host template:

1. Add one of the supported provides, as described in Add a Provider.

2. Go to Farm > Site > RD Session Hosts > Templates tab.

3. In the Tasks drop-down menu, click Add (or click the [+] icon).

4. In the dialog that opens, select a host from which you would like to create a template and click OK.

5. The Create Parallels Template Wizard opens. Each wizard page is described below in the order they appear on the screen.

6. Verify that the Agent is installed and install it manually if needed as described in Step 1: Check and install the Agent. This step only appears if an on-premises Provider is used.

7. Configure the template as described in Step 2: Configure the template.

This section describes how to configure and manage an existing RD Session Host.

Viewing RD Session Hosts based on a specific template

To view the list of RD Session Hosts based on a specific template:

1. Go to Farm > <Site> > RD Session Hosts > Templates.

2. Select a template and click Tasks > Show servers.

Site defaults

Checking the RAS Guest Agent status

A guest RD Session Hosts based on a template must have RAS Guest Agent installed and the agent must match the Parallels RAS version. The agent is installed by default when an RD Session Host is created from a template. If the RD Session Host was created using the native hypervisor tools, it may not have the agent installed in it. In such a case, the RD Session Host will be able to serve only the remote desktop. To enable it to server applications or documents, you'll need to install the agent yourself.

To check if the RAS Guest Agent is installed and up to date:

1. Go to Farm > <Site> > RD Session Hosts > RD Session Hosts.

The RD Session Host template must also have the RAS RD Session Host Agent installed.

To check if the RAS RD Session Host Agent is installed and up to date:

1. Go to Farm > <Site> > RD Session Hosts > Templates.

2. Select a template in the list and then click Tasks > Troubleshooting > Check agent.

Deleting an RD Session Hosts based on a template

Managing RD Session Hosts based on a template that failed preparation

Recreating an RD Session Hosts based on a template

If something happens to a RD Session Hosts based on a template and it becomes unusable, you don't have to delete it and create a new one. Instead, you can recreate it keeping its name, MAC address, and other properties. This way none of the other Site settings, which may rely on a broken RD Session Host, will be affected. Another reason for recreating an RD Session Host is to apply changes made to the template (when you exit from maintenance without executing the Recreate command).

Please note that recreated RD Session Hosts can keep the the following properties:

• MAC address is kept on ESXi, vCenter, Hyper-v, Hyper-v Failover Cluster, Nutanix AHV (AOS), and SC//HyperCore.

• BIOS UUID is kept on ESXi and vCenter.

• DRS groups are kept on vCenter.

To recreate one or more guest RD Session Host:

1. In the Parallels RAS Console, navigate to Farm > <Site> > RD Session Hosts > Templates.

2. To recreate all deployed RD Session Host, click the Tasks drop-down list and choose Recreate all servers.

3. To recreate a specific host (or multiple hosts), click Tasks > Show servers. This will open the dialog which will list RD Session Hosts. Select one or more RD Session Hosts and then click the Tasks > Recreate.

When you recreate a RD Session Host based on a template:

• The procedure deletes the RD Session Host and creates a new one from the same template.

• The new RD Session Host retains the same computer name as the one it replaces.

• If an RD Session Host is running, all unsaved data in its memory will be lost. For this reason, an important data should be saved to an external storage.

To view the list of RD Session Hosts for the current Site:

1. In the RAS Console, navigate to Farm > <Site-name> > RD Session Hosts.

2. The available RD Session Hosts are displayed on the RD Session Hosts tab in the right pane.

You can filter the RD Session Hosts list as follows:

1. Click the magnifying glass icon, which is located on a toolbar above the list.

2. An extra row is displayed at the top of the list where you can type a string in one or more columns that will be used to filter the list.

3. For example, if you want to search for a server by its name, enter the text in the Server column. You can type the entire server name or the first few characters until a match is found. The list will be filtered as you type and only the matching server(s) will be displayed.

4. If you type a filter string in more than one column, they will be combined using the logical AND operator.

5. To remove the filter and display the complete list, click the magnifying glass icon again.

6. If you click the magnifying glass icon one more time, you'll see that the filter that you specified earlier is still there. To remove it completely, simply delete the filter string(s) from the column(s).

Viewing RD Session Host summary

In addition to the RD Session Hosts editor described above, you can also see the summary about the available RD Session Hosts. To do so:

1. In the RAS Console, select the Farm category and then select the Site node in the middle pane.

2. The available servers are displayed in the RD Session Hosts host pool in the right pane.

3. To go to the RD Session Host editor (described above), right-click a server and choose Show in the Editor.

Available menu options

You can perform a number of tasks on the an RD Session Host using menus. To do so, click the Tasks drop-down list and choose a desired option, or right-click a host and choose an option from the context menu.

Please note that not all menu options are available for RD Session Hosts based on a template. If an option is not available for this host type, it will be either disabled or hidden. These include:

• Assign to host pool. Host pool assignment is performed automatically for template-based hosts.

• Delete. Deleting a host (which is a VM) can only be done on the template level (the Host List dialog).

• Control (logon commands). Drain mode is managed automatically by the host pool to which a template-based host belongs.

An RD Session Host must have RAS RD Session Host Agent installed in order to publish remote applications and desktop from it. In addition to this, Remote Desktop Services (formerly Terminal Services) must also be installed.

Normally when you add an RD Session Host to a Site, the RD Session Host Agent and Remote Desktop Services are installed by default. However, if you skipped the installation (or uninstalled the agent or RDS from the server), you can check their status and take appropriate actions if needed.

To check the status of RD Session Host Agent and RDS, do the following:

1. First, check the Status column in the RD Session Hosts list. The column should display "OK". If so, the Agent is installed and functioning properly. If not, read on.

2. In addition to the description, the Status column uses a color code to indicate the agent status as follows:

   • Red — not verified

   • Orange — needs update

   • Green — verified

3. Right-click a server and click Troubleshooting > Check agent in the context menu. The Agent Information dialog opens.

4. If the agent is not installed on the server, click the Install button and follow the instructions on the screen.

After the agent installation is complete, you may need to reboot the RD Session Host. You can do it right from the Parallels RAS Console by selecting the server and clicking Tasks > Control > Reboot.

You can assign an RD Session Host to a different Site in your Farm if needed. Please note that this functionality is only available if you have more than one Site in your Farm.

To change the Site assignment:

1. Right-click an RD Session Host and then click Change Site in the context menu. The Change Site dialog opens.

2. Select a Site in the list and click OK. The server will be moved to the RD Session Hosts list of the target Site (Farm > <new-site-name> > RD Session Hosts).

The server properties dialog consists of tabs, each containing their own specific set of properties. All tabs, except General, have either Group Defaults or Site defaults link, which allows you to view and modify default settings. If you want the properties on a particular tab to inherit default settings, select the Inherit default settings option. When you do, the default settings will be inherited from one of the following:

• Group defaults. Groups are described in Grouping and cloning RD Session Host Servers.

• Site defaults. Note that a group may also inherit Site defaults, but this can be overridden in the group properties dialog where you can specify custom settings for a group.

To view or modify default settings, click the Group Defaults or Site defaults link. Note that each individual tab can inherit default settings independently from other tabs.

To specify custom settings for an RD Session Host, clear the Inherit default settings option and use the controls on a given tab to set the desired options.

To configure an RD Session Host:

1. In the RAS Console, navigate to Farm > <site> > RD Session Hosts.

2. Select a server and click Tasks > Properties.

3. The server properties dialog opens where you can configure the RD Session Host properties.

The dialog is described in the subsections that follow this one.

Select or clear the Enable Server in site option to enable or disable the server. A disabled server cannot serve published applications and virtual desktops to clients.

Other elements on this tab are:

• Server: Specifies the server FQDN or IP address.

• Description: An optional server description.

• Change Direct Address: Select this option if you need to change the direct address that Parallels Client uses to establish a direct connection with the RD Session Host.

Use this tab to configure user profile settings.

To use default settings, select the Inherit default settings option. See Using default settings.

For complete instructions about configuring user profiles, see User profile.

The Optimization tab allows you to specify settings that will be used to optimize the RD Session Host for best performance in a Parallels RAS environment. You can select Windows components, services, and other options that will be disabled, removed, or optimized to ensure a more efficient, streamlined, and improved delivery of virtual apps and desktops.

The Application Packages tab allows you to manage MSIX application packages on RD Session Hosts and groups.

Adding a package to an RD Session Host

Adding a package to a VDI pool

Managing applications installed from MSIX packages

The following actions are available from the Task drop-down list:

• Add: Add a new package to the RD Session Host.

• Retry Staging: Manually trigger re-staging of all added packages.

• Refresh: Refresh the list of the packages.

• Delete: Delete the selected package.

Each RD Session Host in a RAS Farm has an RAS RD Session Host Agent installed through which it communicates with other Parallels RAS components. Use the Agent Settings tab to configure the agent.

To configure the agent, set the options as described below.

Application session lingering

• Disconnect active session after: Specifies the amount of time each session remains connected in the background after the user has closed a remote application. This option is used to avoid unnecessary reconnections with the server.

• Logoff disconnected session after: This setting allows you to control how long it takes for a session to be logged off after it is marked as "disconnected".

Other settings

• Port: Specifies a different remote desktop connection port number if a non-default port is configured on the server.

• Max sessions: Specifies the maximum number of sessions.

• Preferred Connection Broker: Select a Connection Broker to which the RD Session Host should connect. This is helpful when Site components are installed in multiple physical locations communicating through WAN. You can decrease network traffic by specifying a more appropriate Connection Broker.

Allow Client URL/Mail redirection

When a user tries to open a URL or an HTML Mailto link in a remote application, the link can be redirected to the client computer and open in a local default application (a web browser or email client) instead of an application on the remote host. To enable this functionality, select the option and click the Configure button. In the dialog that opens, select one of the following:

• Replace Registered Application: This option uses an alternative method of redirecting a link. It replaces the default web browser and mail client with "dummy" apps on the remote server side. By doing so, it can intercept an attempt to open a link and redirect it to the client computer.

• Support Windows Shell URL namespace objects: The Shell URL namespace objects support means that Parallels RAS can intercept actions in published applications that use the Shell namespace API to open links, which is a standard behavior in most applications. The ability to disable support for Shell URL namespace objects is for compatibility with older versions of Parallels RAS. You may disable this option if you want the behavior of an older version of Parallels RAS (RAS v16.2 or earlier).