Hello friends, I am new to EJB. I have been going thru a book in which it is mentioned that application servers are used for scalability? what exactly is scalability and how can app servers support scalability. before reading i had a conception that app servers are used for load balancing. can anyone explain about this. I guess this question is in the right forum. Thanks for any help. Shekar
The SEI defines scalability as "the ease with which a system or component can be modified to fit the problem area." To be more specific, the scalability property of a J2EE application server means that if your user base doubles, you can still serve the users by adding more hardware into the cluster. If the server would not be scalable, you would not be able to accomodate those extra users (or you could, but only paying a high price for it, e.g. double the users = quadruple the number of hardware).
And the way in which application servers support scalability is through clustering and load balancing. Clustering is the ability to deploy the same application on multiple JVM's, scattered across multiple machines, so that the set of JVM's act (in some way) like one large JVM. Load balancing is the act of spreading requests across those JVM's. Both HTTP requests (for Servlets and Web Services) and RMI-IIOP requests (for EJBs) may be load balanced. Kyle