Microsoft recommends the use of Network Load Balancing (NLB) as the primary and preferred method for improving the scalability and availability of Web applications with multiple servers running IIS. One of the benefits of NLB is that all servers can actively participate in the simultaneous handling of incoming HTTP requests. With one solution you can take advantage of multiple box scalability and make the IIS element of the application highly available at the same time.

 

Simple "Clustering" IIS by clustering the IIS services alone does not always guarantee a high availability solution for Web applications, so is not recommended. The cluster is not aware of the state of the web applications, only IIS, so it could be that the web application is broken but the cluster is unaware of the problem. At a high level, the server role of IIS and the "Failover Clustering Feature" should be installed on all servers hosting the application. The web application files are stored on a shared folder. One initial server is configured, and then scripts are generated to put the other servers into the cluster.

 

The links below contain more detailed information on configuring IIS7 (Windows 2008) for NLB, and provides a guide for setting up such systems: