Windows Server 2008 R2 : Understanding Remote Desktop Services (part 3) - RD Connection Broker & RD Licensing

RD Connection Broker

In Windows Server 2003, the feature named Session Directory was introduced to maintain user connection states across load-balanced Terminal Servers. This feature kept a list of sessions indexed by username. Then, when a user became disconnected from that session and attempted to reconnect, the Session Directory redirected the user back to the same Terminal Server that held their disconnected session.

In Windows Server 2008, the Session Directory was renamed to the Terminal Services Session Broker (TS Session Broker). The renamed TS Session Broker also contains a new feature called TS Session Broker load balancing. Microsoft introduced the load-balancing feature to allow administrators to distribute session loads between Terminal Servers without having to use Windows Network Load Balancing (NLB). A typical deployment for the TS Session Broker load-balancing feature is for Terminal Server farms that consist of 2 to 10 servers.

For Windows Server 2008 R2, TS Session Broker was again renamed, this time to RD Connection Broker. Like before, the RD Connection Broker role service still performs load balancing and ensures that users get connected to the correct Remote Desktop session. However, the RD Connection Broker also supports load balancing and session state management for session-based desktops, virtual desktops, and RemoteApp programs accessed by using RemoteApp and Desktop Connection.

To track user sessions in a load-balanced RD Session Host server farm, an RD Connection Broker server stores information in its local database for each and every session. This session information includes where the session resides, its state, the session ID, and the username associated with the session. Using this information, the RD Connection Broker redirects users with an already existing session to the correct RD Session Host server or virtual desktop.

With RD Connection Broker Load Balancing, users with existing sessions are still redirected to those sessions if they attempt to reconnect to them. However, for new session connections, the RD Connection Broker will attempt to distribute the session load between more-powerful and less-powerful servers in the farm based on an assigned server weight value and which server has the least load.

To configure RD Connection Broker Load Balancing, an administrator must create an A or AAAA record for each RD Session Host in a farm. The hostname for the record is then set to the farm’s name and the IP address to the RD Session Host server that is being added. The RD Connection Broker then uses round-robin DNS to distribute a user’s initial connection to an RD Session Host server farm. After the user has connected and authenticated to the initial RD Session Host server, that server then queries the RD Connection Broker for where to redirect the user to. The final RD Session Host server that is returned from the RD Connection Broker is based on the following two decisions:

• Does the user have an existing session? If so, redirect that user to the RD Session Host server where that session exists.

• If the user doesn’t have an existing session, which RD Session Host server has the least load? Redirect that user to the RD Session Host server with the least load.

In addition, there are also a couple of features that allow an administrator some control over the two previously listed decision paths. First, as mentioned, server weight can be assigned to each RD Session Host server that has been added to the RD Connection Broker. Configuring a server weight allows differences in load to be spread across RD Session Host servers that might not have the same hardware configuration. Less-powerful RD Session Host servers would then have a lower weight and fewer sessions, whereas more-powerful RD Session Host servers would have a higher weight and more sessions. Second, an administrator can also configure an RD Session Host server to act as a dedicated redirector. A dedicated redirector is an RD Session Host server that is configured to process initial session requests, but does not accept any user sessions. By using a dedicated redirector(s), the time associated with the initial connection into a farm and the resulting redirection is decreased, which results in faster logon times.

Windows System Resource Manager

Windows System Resource Manager (WSRM) is a feature in Windows Server 2008 R2 that allows administrators to control how resources are allocated to applications, services, and processes. When being used in conjunction with Remote Desktop Services, WSRM allows administrators to precisely control the amount of resources each user or session is allowed to consume on an RD Session Host server. By limiting resources a session or user can use, an administrator can reduce the chances of a user maxing out an RD Session Host server’s resources, which might impact other users on that server.

Using Network Load Balancing (NLB)

Since Windows 2000 Server Terminal Services, Terminal Services nodes could be “clustered” using Network Load Balancing (NLB) to split the client load across several servers. With the introduction of RD Connection Broker Load Balancing, this clustering technique is no longer the only method by which to facilitate RD Session Host load balancing. As a general recommendation, RD Connection Broker Load Balancing should be used for RD Session Host server farms that need to facilitate load balancing.

RD Licensing

In addition to purchasing a Windows Server 2008 R2 server license, administrators must also have the correct number of Windows Server client access licenses (CALs). When utilizing Remote Desktop Services functionality, an additional set of Terminal Services client access licenses (TS CALs) or Remote Desktop Services client access licenses (RDS CALs) is needed for each user or device. For certain types of deployments, RDS External Connector or Service Providers License Agreement (SPLA) licenses can be purchased as well.

Understanding Remote Desktop Services License Types

The following Remote Desktop Licensing types are available for use:

• RDS Device CAL— This CAL type permits one device (used by any user) to utilize Remote Desktop Services functionality on any server.

• RDS User CAL— This CAL type permits one user (using any device) to utilize Remote Desktop Services functionality on any server.

• RDS External Connector— Using this type of license allows for multiple external users to access a single Remote Desktop server; when multiple servers are being used, additional RDS External Connectors and Windows Server External Connectors must be purchased.

• Service Providers License Agreement (SPLA)— Using this type of license provides a service provider with a more flexible and robust licensing solution when hosting Remote Desktop Services to a number of different organizations and end users.

Understanding Remote Desktop Services Client Access Licensing Mode

When using RDS CALs (Per-User or Per-Device modes), a separate RDS CAL is required for each user or device that is accessing Remote Desktop Services. CALs may be reassigned from one user or device to another. This assignment can be either permanent or temporary, depending on the need at the time.

Understanding Virtual Desktop Infrastructure (VDI) Licensing

To correctly license a VDI environment also requires the purchase of licenses for both the Windows operating system being used for the virtual machine(s) and the infrastructure/management components needed for an end-to-end VDI deployment.

To license Windows as a guest operating system for any VDI environment, regardless of the choice of infrastructure or hypervisor vendor, a Virtual Enterprise Centralized Desktop (VECD) licensing agreement must be purchased. This agreement is available both for client devices that are covered by Software Assurance (VECD for SA) or just VECD for devices such as thin clients.

To license the rest of a VDI environment requires using one of two paths. The VDI infrastructure components can be licensed using RDS CALs, whereas the VDI management components are separately licensed. Or, the environment can be licensed using either Microsoft Virtual Desktop Infrastructure Standard Suite or the Microsoft Virtual Desktop Infrastructure Premium Suite. Both suites are volume license offerings that combine the products for an optimum VDI experience in a value package.

Understanding New RD Licensing Features

The new features that have been introduced in Windows Server 2008 R2 for the RD Licensing role service are discussed in the following sections.

Automatic License Server Discovery No Longer Supported for Remote Desktop Servers

In previous versions of Windows Server, the licensing server was automatically discovered on the network. In Windows Server 2008 R2, automatic discovery is no longer supported. Instead, administrators must now specify the name of a licensing server to use for each RD Session Host server.

Changes to the Licensing Tab in Remote Desktop Server Configuration

When configuring an RD Session Host server, an administrator can use the Licensing tab in the Remote Desktop Server Configuration tool to specify the licensing server. When using this tab, a licensing server can be chosen from a list of servers that have been registered as a service connection point in Active Directory or can be manually defined by entering its name. For cases where more than one license is added, an RD Session Host server will attempt to contact licensing servers in the order in which they appear in the Specified License Servers box.

The Manage RDS CALs Wizard

A new wizard has been introduced in the RD Licensing Manager, which allows the following tasks to be performed:

• Migrate RDS CALs from one licensing server to another.

• Rebuild the RD Licensing database.

It is important to understand that the Manage RDS CALs Wizard can only be used against licensing servers running Windows Server 2008 R2. Therefore, if a licensing server is not running Windows Server 2008 R2, the original CALs on that server should be manually removed as part of the migration process to a Windows Server 2008 R2 licensing server.

Service Connection Point Registration

While installing the RD Licensing role service, the licensing server will attempt to register itself as a Service Connection Point (SCP) in Active Directory. Once registered, the licensing server will then show up as a known licensing server in the Remote Desktop Server Configuration tool’s Licensing tab. If Active Directory is not available during the role service installation, or the SCP registration fails, an administrator must manually register the licensing server by using Review Configuration in the RD Licensing Manager.