TS Session Broker Load Balancing Step-by-Step Guide

Microsoft Corporation

Published: June 2008

Author: Tessa Wooley

Editor: Linda Caputo

AbstractTerminal Services Session Broker (TS Session Broker) is a role service in

Windows Server® 2008 that enables you to load balance sessions in a terminal server farm, and

allows a user to reconnect to an existing session in a load-balanced terminal server farm. The

new TS Session Broker Load Balancing feature enables you to easily distribute the session load

between servers in a load-balanced terminal server farm.

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Contents

TS Session Broker Load Balancing Step-by-Step Guide................................................................5

What new functionality does this feature provide?.......................................................................5

About using DNS round robin......................................................................................................6

TS Session Broker Load Balancing system requirements...........................................................8

Checklist: Deploying TS Session Broker Load Balancing............................................................9

Install the TS Session Broker role service...................................................................................9

Installation prerequisites........................................................................................................10

Installation procedure.............................................................................................................10

Add each terminal server in the farm to the Session Directory Computers local group.............11

Configure TS Session Broker settings for terminal servers in the farm......................................11

Configure TS Session Broker settings by using Group Policy................................................12

Configure TS Session Broker settings by using Terminal Services Configuration..................13

Configure DNS for TS Session Broker Load Balancing.............................................................15

Additional information................................................................................................................16

Configure dedicated redirectors (optional).............................................................................16

Deny logons to a terminal server in a load-balanced farm.....................................................18

Additional references..........................................................................................................18

TS Session Broker Load Balancing Step-by-Step Guide

Terminal Services Session Broker (TS Session Broker) is a role service in the

Windows Server® 2008 operating system that enables you to load balance sessions between

terminal servers in a farm, and allows a user to reconnect to an existing session in a load-

balanced terminal server farm. TS Session Broker stores session state information that includes

session IDs, their associated user names, and the name of the server where each session

resides.

This step-by-step guide describes how to configure the new TS Session Broker Load Balancing

feature.

Note

In Windows Server 2008, the name of the Terminal Services Session Directory feature

was changed to TS Session Broker.

What new functionality does this feature provide?The new TS Session Broker Load Balancing feature enables you to evenly distribute the session

load between servers in a load-balanced terminal server farm. With TS Session Broker Load

Balancing, new user sessions are redirected to the terminal server with the fewest sessions.

Using TS Session Broker to load balance sessions involves two phases. In the first phase, initial

connections are distributed by a preliminary load-balancing mechanism, such as Domain Name

System (DNS) round robin. After a user authenticates, the terminal server that accepted the initial

connection queries the TS Session Broker server to determine where to redirect the user.

In the second phase, the terminal server where the initial connection was made redirects the user

to the terminal server that was specified by TS Session Broker. The redirection behavior is as

follows:

A user with an existing session will connect to the server where their session exists.

A user without an existing session will connect to the terminal server that has the fewest

sessions.

TS Session Broker Load Balancing sets a limit of 16 for the maximum number of pending logon

requests to a particular terminal server. This helps to prevent the scenario where a single server

is overwhelmed by new logon requests; for example, if you add a new server to the farm, or if you

enable user logons on a server where they were previously denied.

The TS Session Broker Load Balancing feature also enables you to assign a relative weight value

to each server. By assigning a relative weight value, you can help to distribute the load between

more powerful and less powerful servers in the farm. For more information, see Configure TS

Session Broker settings by using Terminal Services Configuration.

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Additionally, a new "server draining" mechanism is provided that enables you to prevent new

users from logging on to a terminal server that is scheduled to be taken down for maintenance.

This mechanism provides for the ability to take a server offline without disrupting the user

experience. If new logons are denied on a terminal server in the farm, TS Session Broker will

allow users with existing sessions to reconnect, but will redirect new users to terminal servers that

are configured to allow new logons. For more information, see Deny logons to a terminal server in

a load-balanced farm.

You can enable TS Session Broker Load Balancing through Terminal Services Configuration,

Group Policy, or Windows Management Instrumentation (WMI). If you are using DNS round robin

to distribute initial connections, you must also configure DNS entries for each terminal server in

the farm.

Note

While any load-balancing mechanism can be used to distribute the initial connections,

DNS round robin is the easiest mechanism to deploy. Deploying TS Session Broker Load

Balancing with a network level load-balancing solution such as Network Load Balancing

(NLB) or a hardware load balancer avoids the limitations of DNS, while still taking

advantage of TS Session Broker session-based load balancing, the per server limit on

the number of pending logon requests, and the new "server draining" feature. The

limitations of DNS round robin include the caching of DNS requests on the client, which

can result in clients using the same IP address for each initial connection request, and

the potential for a 30-second timeout delay if a user is redirected to a terminal server that

is offline, but still listed in DNS.

About using DNS round robinTo configure DNS round robin, you must create a host resource record for each terminal server in

the farm that maps to the terminal server farm name in DNS. (The farm name is the virtual name

that clients will use to connect to the terminal server farm.) DNS uses round robin to rotate the

order of the resource records that are returned to the client. This functionality helps to distribute

initial connections across servers in the farm. The initial connection behavior is as follows:

1. An incoming Terminal Services client queries DNS and receives a list of IP addresses for the

farm.

2. The client tries to connect to the first IP address in the list that was returned by DNS.

If the connection fails, the client will automatically try to connect to the next IP address (after

a 30-second timeout delay). This provides a degree of fault tolerance if one of the terminal

servers is unavailable.

The following diagram provides a more detailed representation of the traffic flow. In the

diagrammed scenario, all terminal servers in the farm have host resource records in DNS that

map to the terminal server farm name (“Farm1”). Therefore, any terminal server in the farm can

act as a redirector and process the initial connection requests.

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1. A user on the client computer starts the Remote Desktop Connection (RDC) client. In the

Computer field, they specify the name of the terminal server farm (in this case, Farm1). The

client contacts the DNS server to resolve the Farm1 name to an IP address.

2. The DNS server, which is configured to use round robin to load balance the initial connection

requests, returns the IP addresses that are registered for Farm1 to the client.

3. The client sends the connection request to the first IP address in the list that is returned by

DNS. In this example, this is the IP address of TerminalServer2 (10.0.0.3).

4. TerminalServer2, acting as the redirector, queries the TS Session Broker server to determine

which terminal server the client should log on to.

5. The TS Session Broker server checks its database and does either of the following:

If the user has an existing session, the TS Session Broker server returns the IP address

of the terminal server where the session exists to the redirector.

If the user does not have an existing session, the TS Session Broker server determines

which terminal server in the farm has the lowest load (based on the number of sessions

and the relative server weight value). The TS Session Broker server returns the IP

address of the terminal server with the lowest load to the redirector.

6. The redirector (TerminalServer2) sends the client the IP address of the terminal server that

the client should connect to (in this example, TerminalServer3).

7. The client sends the connection request to TerminalServer3. TerminalServer3 processes the

logon request and the user starts a Terminal Services session.

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8. TerminalServer3 notifies the TS Session Broker server of the successful logon.

Note

For information about how to configure dedicated redirectors that redirect user sessions

but do not accept user logons, see Configure dedicated redirectors (optional).

TS Session Broker Load Balancing system requirementsTo participate in TS Session Broker Load Balancing, the following system requirements apply:

The TS Session Broker server and the terminal servers in the farm must be running Windows

Server 2008. TS Session Broker is available in the Windows Server 2008 Standard operating

system, as well as the Windows Server 2008 Enterprise and Windows Server 2008

Datacenter operating systems.

Note

Windows Server 2003-based terminal servers cannot use the TS Session Broker

Load Balancing feature.

You must configure all terminal servers in the load-balanced farm identically, with the same

available programs.

For clients to use TS Session Broker Load Balancing, they must be running Remote Desktop

Connection (RDC) version 5.2 or later.

In addition, we recommend that you configure all terminal servers in the farm to restrict each user

to a single session. To do this, use either of the following methods:

Configure the Restrict Terminal Services users to a single remote session Group Policy

setting. This policy setting is available in the Computer Configuration\Policies\

Administrative Templates\Windows Components\Terminal Services\Terminal Server\

Connections node of the Group Policy Management Console (GPMC) on a Windows

Server 2008-based domain controller. It is a best practice to group the terminal servers that

are in the same terminal server farm into a single organizational unit (OU), and then configure

this policy setting in a Group Policy object (GPO) that applies to the OU.

Note

If you are using the Local Group Policy Editor, Policies is not part of the node path.

Configure the Restrict each user to a single session setting on each terminal server by

using Terminal Services Configuration. This setting appears under Edit settings, in the

General section.

Checklist: Deploying TS Session Broker Load BalancingTo deploy TS Session Broker Load Balancing, you must complete the following tasks.

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Note

This step-by-step guide describes how to configure TS Session Broker Load Balancing

by using DNS round robin to distribute the initial connections. If you prefer, you can use

NLB or a hardware load balancer to spread the initial connection and authentication load

between multiple terminal servers in the farm.

 

Task Reference

Install the TS Session Broker role service on

the server that you want to use to track user

sessions for a farm.

Install the TS   Session Broker role service

Add the terminal servers in the farm to the

Session Directory Computers local group on

the TS Session Broker server.

Add each terminal server in the farm to the

Session Directory Computers local group

Configure the terminal servers in the farm to

join a farm in TS Session Broker, and to

participate in TS Session Broker Load

Balancing.

Configure TS Session Broker settings for

terminal servers in the farm

Configure DNS round robin entries for terminal

servers in the farm.

Configure DNS for TS Session Broker Load

Balancing

Install the TS Session Broker role serviceYou must install the TS Session Broker role service on the server that you want to use to track

user session information for a load-balanced terminal server farm. You can use a single

TS Session Broker server to track user sessions across multiple farms, as there is minimal

performance overhead.

The Windows Server 2008-based server where you install the TS Session Broker role service

does not have to be a terminal server or have Remote Desktop enabled. It is considered a best

practice to install the TS Session Broker role service on a back-end infrastructure server, such as

a file server. If you install the role service on a server that is not a terminal server, the Terminal

Services Session Broker service will not be affected when you need to perform maintenance on

terminal servers in the farm.

When you install the TS Session Broker role service, the following changes occur on the local

computer:

The Terminal Services Session Broker service is installed. By default, the service is set to

Started and to Automatic.

The Session Directory Computers local group is created.

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Installation prerequisitesThe server where you install TS Session Broker must be a member of a domain.

Note

If you install the TS Session Broker role service on a domain controller, the Session

Directory Computers group will be a domain local group and will be available on all

domain controllers.

Installation procedureMembership in the local Administrators group is the minimum required to complete this

procedure.

To install TS Session Broker

1. Open Server Manager. To open Server Manager, click Start, point to Administrative

Tools, and then click Server Manager.

2. If the Terminal Services role is already installed:

a. Under Roles Summary, click Terminal Services.

b. Under Role Services, click Add Role Services.

c. On the Select Role Services page, select the TS Session Broker check box, and

then click Next.

If the Terminal Services role is not already installed:

a. Under Roles Summary, click Add Roles.

b. On the Before You Begin page of the Add Roles Wizard, click Next.

c. On the Select Server Roles page, select the Terminal Services check box, and

then click Next.

d. Review the Terminal Services page, and then click Next.

e. On the Select Role Services page, select the TS Session Broker check box, and

then click Next.

3. On the Confirm Installation Selections page, click Install.

4. On the Installation Results page, confirm that the installation succeeded, and then click

Close.

Add each terminal server in the farm to the Session Directory Computers local groupFor terminal servers to use TS Session Broker, you must add the computer account for each

terminal server in the farm to the Session Directory Computers local group on the TS Session

Broker server.

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Membership in the local Administrators group is the minimum required to complete this

procedure.

Important

You must perform this procedure on the server where you installed the TS Session

Broker role service.

To add terminal servers to the Session Directory Computers local group

1. On the TS Session Broker server, click Start, point to Administrative Tools, and then

click Computer Management.

2. In the left pane, expand Local Users and Groups, and then click Groups.

3. In the right pane, right-click the Session Directory Computers group, and then click

Properties.

4. Click Add.

5. In the Select Users, Computers or Groups dialog box, click Object Types.

6. Select the Computers check box, and then click OK.

7. Locate and then add the computer account for each terminal server that you want to add.

8. When you are finished, click OK.

Configure TS Session Broker settings for terminal servers in the farmYou can configure a terminal server to join a farm in TS Session Broker and to participate in

TS Session Broker Load Balancing by using Group Policy or the Terminal Services Configuration

tool. However, you must use Terminal Services Configuration to configure the following settings:

The IP addresses to be used for reconnection.

The relative weight of the server when using TS Session Broker Load Balancing.

For information about how to configure the settings by using Group Policy, see Configure TS

Session Broker settings by using Group Policy. Configuring the settings by using Group Policy is

a recommended best practice.

For information about how to configure the settings by using Terminal Services Configuration, see

Configure TS Session Broker settings by using Terminal Services Configuration.

Important

Group Policy settings take precedence over configuration settings in the Terminal

Services Configuration snap-in and those that are made by using the Terminal Services

WMI provider.

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Configure TS Session Broker settings by using Group PolicyTo assign TS Session Broker settings through Group Policy, it is a best practice to group the

terminal servers that are in the same terminal server farm into a single OU in Active Directory

Domain Services (AD DS). Then, configure the TS Session Broker settings in a GPO that applies

to the OU.

Note

For the TS Session Broker settings to be effective on a server, the server must have the

Terminal Server role service installed.

The following procedure describes how to configure TS Session Broker Group Policy settings by

using the Group Policy Management Console (GPMC) on a Windows Server 2008-based domain

controller.

To change Group Policy settings for a domain or an OU, you must be logged on as a member of

the Domain Admins, Enterprise Admins, or the Group Policy Creator Owners group, or have

been delegated the appropriate control over Group Policy to complete this procedure.

To apply TS Session Broker settings to an Active Directory OU

1. To start the GPMC, click Start, point to Administrative Tools, and then click Group

Policy Management.

2. In the left pane, locate the OU that contains the terminal servers.

3. To modify an existing GPO for the OU, expand the OU, and then click the GPO.

To create a new GPO, follow these steps:

a. Right-click the OU, and then click Create a GPO in this domain, and link it here.

b. In the Name box, type a name for the GPO, and then click OK.

c. In the left pane, click the new GPO.

4. In the right pane, click the Settings tab.

5. Right-click Computer Configuration, and then click Edit.

6. In the left pane, under Computer Configuration, expand Policies, expand

Administrative Templates, Windows Components, Terminal Services, and Terminal

Server, and then click TS Session Broker.

7. In the right pane, double-click the Join TS Session Broker policy setting, click Enabled,

and then click OK.

8. Double-click the Configure TS Session Broker farm name policy setting, and then do

the following:

a. Click Enabled.

b. In the TS Session Broker farm name box, type the name of the farm in TS Session

Broker that you want to join, and then click OK.

Important

TS Session Broker uses a farm name to determine which servers are in the

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same terminal server farm. You must use the same farm name for all servers

that are in the same load-balanced terminal server farm. Although the farm

name in TS Session Broker does not have to be registered in AD DS, it is

recommended that you use the same name that you will use in DNS for the

terminal server farm. (The terminal server farm name in DNS represents the

virtual name that clients will use to connect to the terminal server farm.) If

you type a new farm name, a new farm is created in TS Session Broker and

the server is joined to the farm. If you type an existing farm name, the server

joins the existing farm in TS Session Broker.

9. Double-click the Configure TS Session Broker server name policy setting, and then do

the following:

a. Click Enabled.

b. In the TS Session Broker server name box, type the name of the server where you

installed the TS Session Broker role service, and then click OK.

10. Double-click the Use TS Session Broker load balancing policy setting, click Enabled,

and then click OK.

11. Optionally, if you are using a hardware load balancer that supports token redirection,

double-click Use IP Address Redirection and configure the setting. See the Group

Policy Explain text for more information.

Note

To configure TS Session Broker settings by using local Group Policy, use the Local Group

Policy Editor. To start the Local Group Policy Editor, click Start, click Run, type

gpedit.msc, and then click OK. To configure local Group Policy settings, you must be a

member of the Administrators group on the local computer or you must have been

delegated the appropriate authority.

Configure TS Session Broker settings by using Terminal Services ConfigurationYou can configure a terminal server to join a farm in TS Session Broker and to participate in

TS Session Broker Load Balancing by using Terminal Services Configuration.

Note

The following steps are only applicable if the Terminal Server role service is installed.

Membership in the local Administrators group is the minimum required to complete this

procedure.

To configure TS Session Broker settings by using Terminal Services Configuration

1. Start Terminal Services Configuration. To do this, click Start, point to Administrative

Tools, point to Terminal Services, and then click Terminal Services Configuration.

2. In the Edit settings area, under TS Session Broker, double-click Member of farm in

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TS Session Broker.

3. On the TS Session Broker tab, click to select the Join a farm in TS Session Broker

check box.

4. In the TS Session Broker server name or IP address box, type the name or the IP

address of the TS Session Broker server.

Note

The TS Session Broker server is the server where you installed the TS Session

Broker role service.

5. In the Farm name in TS Session Broker box, type the name of the farm that you want

to join in TS Session Broker.

Important

TS Session Broker uses a farm name to determine which servers are in the

same terminal server farm. You must use the same farm name for all servers that

are in the same load-balanced terminal server farm. Although the farm name in

TS Session Broker does not have to be registered in AD DS, it is recommended

that you use the same name that you will use in DNS for the terminal server

farm. (The terminal server farm name in DNS represents the virtual name that

clients will use to connect to the terminal server farm.) If you type a new farm

name, a new farm is created in TS Session Broker and the server is joined to the

farm. If you type an existing farm name, the server joins the existing farm in

TS Session Broker.

6. To participate in TS Session Broker Load Balancing, select the Participate in Session

Broker Load-Balancing check box.

7. Optionally, in the Relative weight of this server in the farm box, modify the server

weight. By default, the value is 100. The server weight is relative. Therefore, if you assign

one server a value of 100, and one a value of 200, the server with a relative weight of

200 will receive twice the number of sessions.

8. Verify that you want to use IP address redirection. By default, the Use IP address

redirection (recommended) setting is enabled. If you clear the check box, the server

switches to token redirection mode.

9. In the Select IP addresses to be used for reconnection box, click to select the check

box next to each IP address that you want to use. When you select the IP addresses to

use, consider the following:

Only the first selected IPv4 address will be used by clients that are running RDC 5.2

and earlier.

Using IPv6 addresses is not recommended if the terminal server farm contains

servers that are running Windows Server 2003.

10. When you are finished, click OK.

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Configure DNS for TS Session Broker Load BalancingTo configure DNS round robin for TS Session Broker Load Balancing, you must map the IP

address of each terminal server in the farm to the terminal server farm name in DNS.

The following procedure provides the steps to configure DNS on a Windows Server 2008-based

domain controller.

You must be a member of the Domain Admins, Enterprise Admins, or the DnsAdmins group

to complete this procedure.

To add DNS entries for each terminal server in the farm

1. Click Start, point to Administrative Tools, and then click DNS.

2. Expand the server name, expand Forward Lookup Zones, expand the domain name,

and then click the appropriate zone.

3. Right-click the zone, and then click New Host (A or AAAA).

4. In the Name (uses parent domain name if blank) box, type the terminal server farm

name.

The farm name is the virtual name that clients will use to connect to the terminal server

farm. For management purposes, it is recommended that you use the same farm name

that you specified when you configured the terminal servers to join a farm in TS Session

Broker.

Important

Do not use the name of an existing server for the farm name.

5. In the IP address box, type the IP address of a terminal server in the farm.

6. Click Add Host, and then click OK when you receive the message that the host record

was successfully created.

7. Repeat steps four through six for each terminal server in the farm. For each DNS entry,

ensure that you specify the same farm name in the Name (uses parent domain name if

blank) box. For example, if you have three terminal servers in a farm named FARM1,

with IP addresses of 192.168.1.20, 192.168.1.21, and 192.168.1.22, the entries would

look similar to the following:

Farm1 Host(A) 192.168.1.20

Farm1 Host(A) 192.168.1.21

Farm1 Host(A) 192.168.1.22

8. When you are finished, click Done.

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Additional information

Configure dedicated redirectors (optional)When you register the IP address of each terminal server in the farm to a single terminal server

farm name in DNS, incoming Terminal Services clients will try to connect to the first IP address for

the farm name that is returned by DNS. The terminal server that receives this initial connection

request acts as the redirector.

To increase session redirection performance in a large terminal server farm, you can configure

terminal servers to be dedicated redirectors. These servers will process incoming requests, but

will not accept user sessions. To configure dedicated redirectors, you must do the following:

1. Create DNS round robin entries for the terminal servers that you want to use as dedicated

redirectors. When you do so, you must map the IP address of each terminal server that you

are using as a dedicated redirector to the terminal server farm name in DNS. (The farm name

is the virtual name that clients will use to connect to the terminal server farm.) The farm name

must not match an existing server name in AD DS.

2. Configure the servers to deny new user logons. For more information about how to deny new

user logons, see Deny logons to a terminal server in a load-balanced farm.

Because these dedicated redirectors have no user sessions, they do not require roaming profiles

or any installed programs. This enables a faster logon experience, and makes the server easier

to manage and more reliable.

The following diagram provides a more detailed representation of the traffic flow. In the

diagrammed scenario, two terminal servers are deployed as dedicated redirectors. (In a large

terminal server farm, you may want to have more than two dedicated redirectors.) The terminal

servers will redirect initial connection requests, but will not host any sessions (that is, they are

configured to deny new user logons). Only the two redirectors have host resource records in DNS

that map to the terminal server farm name. All terminal servers in the farm (including the

redirectors) are configured to use the same farm in TS Session Broker (in the Terminal Services

Configuration settings).

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1. A user on the client computer starts the RDC client. In the Computer field, they specify the

name of the terminal server farm (in this case, Farm1). The client contacts the DNS server to

resolve the Farm1 name to an IP address.

2. The DNS server, which is configured to use round robin to load balance the initial connection

requests, returns the IP addresses that are registered for Farm1 (in this case, the IP

addresses of the two redirectors).

3. The client sends the connection request to the first IP address in the list that is returned by

DNS. In this example, this is the IP address of Redirector2 (10.0.0.3).

4. The redirector (Redirector2) queries the TS Session Broker server to determine which

terminal server the client should log on to.

5. The TS Session Broker server checks its database and does either of the following:

If the user has an existing session, the TS Session Broker server returns the IP address

of the terminal server where the session exists to the redirector.

If the user does not have an existing session, the TS Session Broker server determines

which terminal server in the farm has the lowest load (based on the number of sessions

and the relative server weight value). The TS Session Broker server returns the IP

address of the terminal server with the lowest load to the redirector.

6. Redirector2 sends the client the IP address of the terminal server that the client should

connect to (in this example, TerminalServer5).

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7. The client sends the connection request to TerminalServer5. TerminalServer5 processes the

logon request and the user starts a Terminal Services session.

8. TerminalServer5 notifies the TS Session Broker server of the successful logon.

Note

In the diagram, TS Session Broker is installed on a separate server. You can install

TS Session Broker on one of the terminal servers that will act as a dedicated redirector.

Deny logons to a terminal server in a load-balanced farmIn Windows Server 2008, you can configure a terminal server to deny logon requests from new

users. With the ability to deny logons from new users to specific servers in a farm, you can

maintain your terminal server environment without disrupting end-user service. If you configure a

terminal server to deny new logons, the following behavior occurs:

Users with existing sessions can still reconnect to the server. Only new logons to that server

are denied. However, an administrator can still log on to the server locally to perform

maintenance on the server.

Note

An administrator can also connect remotely by starting the RDC client from the

command line with the /admin option (mstsc /admin).

If you are using TS Session Broker Load Balancing, TS Session Broker will redirect new

users to other servers in the farm, where new user logons are enabled.

Before you take a server down for maintenance, you can notify users with existing sessions to log

off from the server by using Terminal Services Manager to send a message.

To deny new user logons

1. Click Start, point to Administrative Tools, point to Terminal Services, and then click

Terminal Services Configuration.

2. In the Edit settings area, double-click User logon mode under General.

3. On the General tab, click either of the following:

Allow reconnections, but prevent new logons

Allow reconnections, but prevent new logons until the server is restarted

4. Click OK.

When you are finished doing maintenance, ensure that Allow all connections is

selected.

Additional references

For information about how to configure a load-balanced terminal server farm by using

TS Session Broker and NLB, see the Step-by-Step Guide for Configuring Network Load

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Balancing with Terminal Services in Windows Server 2008 (http://go.microsoft.com/fwlink/?

LinkID=80406).

For information about Terminal Services Session Directory in Windows Server 2003, see

Session Directory and Load Balancing Using Terminal Server (http://go.microsoft.com/fwlink/?

LinkID=80740).

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