Planning for federation server proxy capacity

Applies To: Windows Server 2003 R2

Capacity planning for federation server proxies helps you estimate the following:

• The appropriate hardware requirements for each federation server proxy

• The number of federation servers and federation server proxies to place in each organization

Federation server proxies provide security tokens from a protected federation server in the corporate network to federated users. A federation server proxy does not actually sign tokens or access trust policy. Therefore, the hardware requirements for the federation server proxy are usually lower than the hardware requirements for a federation server. Because every request to a federation server proxy results in a request to a federation server or federation server farm, capacity planning for federation servers and federation server proxies must be performed in parallel.

Estimating the peak sign-ins per second for the federation server proxy requires an understanding of the usage patterns of the federated users that will be signing in through the federation server proxy. In many deployments, the federated users who sign in using the federation server proxy are located on the Internet. You can estimate the peak sign-ins per second by looking at the usage patterns of these federated users on the existing Web applications that will be protected by Active Directory Federation Services (ADFS).

Determining peak sign-in capacity

The following table shows test lab results that the ADFS product team used to measure the peak capacity of sign-in requests to an account federation server proxy. The table also shows the impact on CPU consumption for the federation server proxy and the federation server. All sign-ins against the account federation server proxy for the tests used forms-based authentication. Secure Sockets Layer (SSL) client authentication was not tested. Because each request to the federation server proxy generates a request from the proxy to the federation server, the CPU consumption of the federation server is shown here as well.

Peak sign-ins per second for the account federation server proxy and the account federation server

Example

You have 7200 Internet customers that use a federated purchasing application (named "Widgetbrowsing") to shop for widgets that your company makes. Previous analysis of the application logs indicates that Widgetbrowsing peaks at 50 requests per second every day. Because this is an Internet scenario, users sign in through forms-based authentication on a federation server proxy. The previous table indicates that one ADFS server, similar to the server that the Microsoft ADFS product team used for testing, can easily handle the 50-request-per-second load. However, the business depends on customers being able to sign in and browse widgets to purchase. This situation demands high availability. Therefore, you deploy a small federation server farm, containing at least two federation servers, and a small federation server proxy farm, containing at least two federation server proxies to balance the load and to prevent a single point of failure. Depending on usage, you might be able to scale down your federation server proxies slightly because your organizational load is much less than the peak capacity of the server that the ADFS product team used in its tests.