Websphere's tight coupling

When you have a lot of competition, you have to make yourself stick out.  In the software development world, this often means having more features than your competition.  In Websphere's case, adding more features has been more of a hindrance in the long term.  This is because Websphere tightly couples features that were supposed to be module.  When you tightly couple the modular features, you make it harder to incrementally upgrade.  This has caused people to start using lighter weight Servlet containers as opposed to using full J2EE-compliant application servers.

Websphere Application Server (WAS) is a J2EE-compliant application server.  It bundles a lot of Java libraries with the product though.  This can come in handy since you don't have to find 3rd party libraries if you want to use one of the various JSR extensions.  The prime example is Java Server Faces (JSF).  WAS 6.1 comes with an IBM implementation of JSF 1.1_01.  It even comes with a component library that gives you extra components that are not part of JSF.  This can be a great selling point.  You buy one product and you get other products for free.  This selling point yielded early sales.  Those companies eventually discovered the problem with IBM JSF implementation: you cannot upgrade JSF independently of WAS.  WAS comes with a jar called webcontainer.jar.  This jar is an Uber jar of the various JSRs.  It has the servlet api and implementation.  It has some WAS internals.  It also contains the JSF api and implementation.  This means you cannot replace or upgrade the JSF implementation without upgrading WAS.

This is why more and more companies are migrating to Tomcat.  It does not come with JSF.  It only implements the basic J2EE JSRs.  If you need one of the features that a full appserver has, you can download an implementation of that JSR.  You can download one of the open source JSF implementations.  If you need to upgrade your JSF implementation, you don't have to upgrade Tomcat as well.  This allows a company to phase in an upgrade.

This separation is part of the reason companies are flocking away from Websphere towards Tomcat.  Tomcat's lack of features is its main feature.  It does a small set of tasks, and it does it well.  Also, due to the open source nature of the software, you can buy support from multiple vendors.  There is no vendor lock in.  Tomcat is a great example of "less is more."