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 RAS Template by utilizing the VDI functionality, which is available in Parallels RAS. 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 page, select Enable Group in site to enable the group. Type a name and description for the group.

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

• Specify a RAS Template on which the servers are based. This will include all RD Session Hosts that have been or will be created from a selected template. To do so, select the RD session hosts based on a RAS Template option and then select a template from the drop-down list. Note that you need to create a RAS Template of type RD Session Host before you can select it here. For more information, see the Using RAS Templates subsection below.
• 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.

Using RAS Templates

RAS Templates of type RD Session Host utilize the VDI functionality available in Parallels RAS. A template is based on a virtual machine (also known as VM or guest VM) running on a hypervisor. When you create a RAS Template, you select a preconfigured VM with the operating system and resources that you intend to publish 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 essentially 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 chapter. Once you are familiar with adding and configuring a VDI host, read the Parallels RAS Templates section which explains how to create a RAS Template of type RD Session Host.

After you select a RAS Template in the Group Properties dialog, click the RAS Template Settings tab page to specify additional properties described below.

Send a request to the RAS Template when the workload threshold is above (%): Specifies the group workload threshold at which one or more additional servers (guest VMs) should be created from the template. 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 RAS 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 in the Default Server Properties dialog and it's 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 Session 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: The number of servers that the template should create per single request from the group. This setting works together with the Send a request to the RAS Template when the workload threshold 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.

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

When you save the 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 "RAS Template error" event is triggered and the administrator will receive an alert message.

Drain and unassign servers from group when workload is below (%):  Specifies the group workload percentage value at which one or more servers should be switched to drain mode or unassigned from the group. 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.

Note: Parallels recommends setting viable timeouts for idle time and disconnected sessions either in Windows Group Policies or Default Server Properties to make the drain mode effective.

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 page, right-click a server and choose Remove from group.
• On the Groups tab page, 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 RAS Template:

1. Go to the Groups tab page.
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.