What Is WebSphere Application Server?

Application servers are java programs that serve active content to web browsers. Active content is information that changes over time. The balance in your checkbook is an example of active content. It changes every time you write a check or make a deposit. Stock and bond prices, inventory levels, the number of people in a pub at any given moment, the position of an airplane as it flies to its destination -- these are all examples of active content. If you want to publish this kind of information on a web site, you have to do more than write plain HTML. You have to write a computer program that

• knows where the information you need can be found
• finds the information you need
• generates the HTML that will present your information
• sends that information to a web browser

That is the kind of program that runs on an application server. There are several application servers.

• Resin
• JBoss
• Geronimo See also this IBM developerWorks article
• WebLogic See also this Wikipedia article
• WebSphere Application Server

All of those application servers are fine products. Each of them serves a need. Most of them are meant to either stand alone or cluster in small groups of servers. One of them -- WebSphere Application Server -- is not just a single server. It is, instead, a network of potentially thousands of servers all providing small pieces of a very large web site. In this article and some related articles, we are going to examine pieces of WebSphere Application Server. It is convenient to think of WebSphere Application Server in three parts:

• a part that produces content. This part has a lot in common with all the other application servers. This article describes how WebSphere Application Server produces content
• a part that controls, configures and manages the thousands of individual servers that make up WebSphere Application Server. This part is a lot more highly developed than the other application servers. This is the part that allows WebSphere Application Server to scale. When IBM talks about Network Deployment, they are talking about this capability.
• a part that balances very high volumes of traffic across very large network of many servers. When IBM talks about eXtended Deployment, they are talking about this capability. This article describes WebSphere Application Server XD