Servlets are clustered in this application by putting a single web server in front of the application server cluster. The HTTP session state is replicated across the cluster members.
Alternatively, you can pass state information back and forth between server and client in cookies. This is a heavyweight solution, but eliminates the possibility of a web server bottleneck.
Another mechanism to cluster servlets uses the application’s workspaces to hold a servlet session’s state and pass only a key to the workspace back and forth in a cookie. This solution provides the same benefit as the previous solution without the excess network traffic.