Federation Server Farm Using WID
The default topology for Active Directory Federation Services (AD FS) is a federation server farm, using the Windows Internal Database (WID), that consists of up to five federation servers hosting your organization's Federation Service. In this topology, AD FS uses WID as the store for the AD FS configuration database for all federation servers that are joined to that farm. The farm replicates and maintains the Federation Service data in the configuration database across each server in the farm.
The act of creating the first federation server in a farm also creates a new Federation Service. When you use WID for the AD FS configuration database, the first federation server that you create in the farm is referred to as the primary federation server. This means that this computer is configured with a read/write copy of the AD FS configuration database.
All other federation servers that you configure for this farm are referred to as secondary federation servers because they must replicate any changes that are made on the primary federation server to the read-only copies of the AD FS configuration database that they store locally.
Note
We recommend the use of at least two federation servers in a load-balanced configuration.
Deployment considerations
This section describes various considerations about the intended audience, benefits, and limitations that are associated with this deployment topology.
Who should use this topology?
Organizations with 100 or fewer configured trust relationships that need to provide their internal users (logged on to computers that are physically connected to the corporate network) with single sign-on (SSO) access to federated applications or services
Organizations that want to provide their internal users with SSO access to Microsoft Online Services or Microsoft Office 365
Smaller organizations that require redundant, scalable services
Note
Organizations with larger databases should consider using the Federation Server Farm Using SQL Server deployment topology, which is described later in this section. Organizations with users who log in from outside the network should consider using either the Federation Server Farm Using WID and Proxies topology or the Federation Server Farm Using SQL Server topology.
What are the benefits of using this topology?
Provides SSO access to internal users
Data and Federation Service redundancy (each federation server replicates changes to other federation servers in the same farm)
The farm can be scaled out by adding up to five federation servers
WID is included with Windows; therefore, no need to purchase SQL Server
What are the limitations of using this topology?
A WID farm has a limit of 30 federation servers. For more information, see AD FS Deployment Topology Considerations.
A WID farm does not support token replay detection or artifact resolution (part of the Security Assertion Markup Language (SAML) protocol).
Server placement and network layout recommendations
When you are ready to start deploying this topology in your network, you should plan on placing all of the federation servers in your corporate network behind a Network Load Balancing (NLB) host that can be configured for an NLB cluster with a dedicated cluster Domain Name System (DNS) name and cluster IP address.
Note
This cluster DNS name must match the Federation Service name, for example, fs.fabrikam.com.
The NLB host can use the settings that are defined in this NLB cluster to allocate client requests to the individual federation servers. The following illustration shows how the fictional Fabrikam, Inc., company sets up the first phase of its deployment using a two-computer federation server farm (fs1 and fs2) with WID and the positioning of a DNS server and a single NLB host that is wired to the corporate network.
Note
If there is a failure on this single NLB host, users will not be able to access federated applications or services. Add additional NLB hosts if your business requirements do not allow having a single point of failure.
For more information about how to configure your networking environment for use with federation servers, see Name Resolution Requirements for Federation Servers in the AD FS Design Guide.