Grouping and cloning RD Session Hosts

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

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

• They simplify the management of published resources and are highly recommended in multi-server environments.
• They allow you to use RD Session Hosts created from a template by utilizing the VDI infrastructure. More on this later in this section.

Note that an RD Session Host can be a member of one group only. You cannot add the same server to multiple groups.

Creating a group

To create an RD Session Host group:

1. In the RAS console, navigate to Farm > <Site> > RD Session Hosts.
2. Click the Groups tab.
3. Click Tasks > New Group (or click the [+] icon). To modify an existing group, right-click it and then choose Properties in the context menu.
4. The Group Properties dialog opens where you can specify the group settings as described below.

On the General tab, select Enable Group in site to enable the group. Type a name and an optional description for the group.

You now need to add one or more RD Session Hosts to the group. You can do this by using the following options (both can be used at the same time):

• Specify a template on which the RD Session Hosts are based. To do so, select the RD session hosts based on a template option and then select a template from the drop-down list. Note that you need to create a template of type RD Session Host before you can select it here. Templates of type RD Session Host utilize the VDI functionality available in Parallels RAS. A template is based on a virtual machine running on a hypervisor or a cloud-based VDI provider. When you create a template, you select a preconfigured VM with the operating system and applications already installed. Individual hosts (VMs) are then created as clones of the template. The clones can be created in advance or on as-needed basis (configurable when you create a template). This functionality allows you to create and configure an RD Session Host running in a virtual machine and then create as many copies of it as you require. For the complete information about using VDI in Parallels RAS see the VDI and Virtual Desktops chapter. Once you are familiar with adding and configuring a VDI provider, read the Templates section which explains how to create a template of type RD Session Host.
• Add servers manually one by one by clicking Tasks > Add and then selecting a server from the list. You can also add a server later by right-clicking it in the main list and choosing Assign to group.

Autoscale

When you select the RD session hosts based on a template option (see above), the Autoscale tab appears in the Group Properties dialog. The settings on this tab determine how RD Session Hosts are created from the specified template. The settings are described below.

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

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

• If the template is used by a single group, then this number can be up to the "Maximum guest VMs" setting of the template.
• If two or more groups share the same template, then the combined number from all groups must be less or equal to the "Maximum guest VMs" settings of the template.

When you save a group, a validation will be performed against other groups (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 servers from template 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 group (if not already available). The group workload percentage is calculated using the following formula:

Group Workload = (Current Sessions / Max Sessions) * 100

In the formula above:

• Current Sessions is the total number of all sessions on all servers in the group. This includes static (standalone) servers and servers created from the template (guest VMs). 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 group) and the maximum number of sessions allowed for the group.

Consider the following examples:

RAS Group 1 — mixed server types (static and guest VMs), 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: Guest VM
• RDSH-4, Status: Drain Mode, Max sessions 10, Current Sessions: 3, Type: Guest VM

For the group 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 Group 2 — mixed server types (static and guest VMs), different agent status:

• RDSH-1, Status: OK, Max Sessions 10, Current Sessions: 0, Type: Guest VM
• RDSH-2, Status: OK, Max Sessions 10, Current Sessions: 2, Type: Guest VM
• RDSH-3, Status: Not Verified, Max sessions 10, Current Sessions: 0, Type: Guest VM

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

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

Number of servers to be added to the group 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 group 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 unassign servers from group 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 "remains below this level" field, excessive hosts will be switched to drain mode or unassigned from the group. 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 group. At that point, the server becomes available to other groups on demand.

Tip: Servers are unassigned from the group 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 group.

Note: Parallels recommends setting viable timeouts for idle time and disconnected sessions either in Windows Group Policies or in the Site Default Properties dialog to make the drain mode effective. GPOs can be used to forcibly log off a user session, however this should be used carefully as this may result in data loss.

Using group defaults

RD Sessions Hosts assigned to a group have various settings that they can inherit from the group 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 group 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 group inherit these settings. The RD Session Hosts assigned to the group will therefore also inherit Site defaults. This is the default scenario for a new group. Site defaults can be configured by navigating to Farm > <Site> > RD Session hosts and clicking Tasks > Site defaults.
• Configure default settings for a given group. This way you can have multiple groups, each having its own group defaults (different from Site defaults). Therefore, the servers assigned to a group will inherit the group's defaults.

To configure default settings for a group, open the Group 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 group will inherit these settings. Note that inheritance works independently for each individual tab on the group properties dialog.

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

Removing a server from a group

To remove a regular RD Session Host from a group, do one of the following:

• On the RD Session Hosts tab, right-click a server and choose Remove from group.
• On the Groups tab, right-click a group and choose Properties. In the Group Properties dialog, select a server and click Tasks > Delete.

To remove an RD Session Host that was added to a group from a template:

1. Go to the Groups tab.
2. Select a group and click Tasks > Properties.
3. In the Group Properties dialog, select a server and click Tasks > Delete.

Note that this is the only place in the RAS Console where you can remove an RD Session Host of this type from a group. Please also note that when you delete such a host, it is drained first and only then unassigned from the group, which may take a considerable amount of time.

After you create a group and later publish resources from it, you can view the list of resources by right-clicking a group and choosing Show published resources (or click Tasks > Show Published Resources). For more information, see Viewing published resources hosted by RD Session Hosts.