More and more mission-critical and large scale applications are now running on Java 2, Enterprise Edition (J2EE). Those mission-critical applications such as banking and billing ask for more high availability (HA), while those large scale systems such as Google and Yahoo ask for more scalability. The importance of high availability and scalability in today's increasingly inter-connected world can be proved by a well known incident: a 22-hour service outage of eBay in June 1999, caused an interruption of around 2.3 million auctions, and made a 9.2 percent drop in eBay's stock value.
J2EE clustering is a popular technology to provide high available and scalable services with fault tolerance. But due to the lack of support from the J2EE specification, J2EE vendors implement clustering differently, which causes a lot of trouble for J2EE architects and developers. Following questions are common:
- Why are the commercial J2EE Server products with Clustering capabilities so expensive? (10 times compared with no clustering capabilities)
- Why does my application built on stand-alone J2EE server not run in a cluster?
- Why does my application run very slowly in a cluster while much faster in non-clustered environment?
- Why does my cluster application fail to port to other vendors' server?
The best way to understand the limitations and considerations is to study their implementations and uncover the hood of J2EE clustering.
http://www.theserverside.com/articles/content/J2EEClustering/article.html
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