>Has anyone written software for a clustered server system? Any suggestions on white papers or books on writing software for this type of server system?
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What type of application will you be hosting on the cluster?

Where I work we've just recently moved our app from a single server to a cluster. The migration was completely transparent. No changes were made to the client portion (a Windows Form app) nor to the server side components. In our case, it helped that all the middle tier business objects are web service classes so the interaction between the client and the server was always stateless, which is very (very) important when you have a cluster.