[CSS] Apache Geronimo Architecture and Community by Bruce Snyder
The main reason that Geronimo was started was to have a BSD-style licensed Java application server. The other two open-source application servers are JOnAS and JBoss, both of which are LGPL. The advantage of having a BSD/Apache licensed container is that companies can put it into their products, or develop products with it - w/o worrying about licensing issues. Bruce says IBM just validated the goals of Geronimo with their WebSphere Community Edition.
Geronimo's architecture is designed around GBeans - which are services that are pluggable inside of the kernel. To learn more about GBeans, see Jeff Genender's article "Integrate third-party components into Geronimo". The GBean is an IoC container in itself. Bruce is now showing a GBean Descriptor for ActiveMQ. There are only a few main elements in this XML file: multiple <dependency> elements and <gbean> elements. The dependency element refers to a JAR and the idea was borrowed from the Maven project.
Bruce, the poster-boy for Maven 2 only made it 15 minutes before he mentioned Maven. 
For more information about integrating ActiveMQ in Geronimo, see Sing Li's article "Magic with JMS, MDBs, and ActiveMQ in Geronimo".
Deployers vs. Builders: Deployers are J2EE specific, Builders are Geronimo specific. The Geronimo Deployer is JSR-88 compliant and handles both deployment and distribution. Personally, I'm a little disappointed that Geronimo doesn't support hot-deploy out-of-the-box, but I can understand their desire to be spec-compliant first, and developer-friendly 2nd. After all, it is an IBM product.
Geronimo's deployer is currently a script that you can pass arguments into. There is also a webapp console (developed and donated by Gluecode) that's based on portlets. It uses JetSpeed under the covers and looks to be a pretty slick little webapp. Bruce started up Geronimo and showed us the console UI - it appears Geronimo's default footprint is about 20 MB.
Custom Assemblies: One of the nice things about Geronimo is that it's so configurable. Because of it's architecture, you can easily create custom assemblies. Here's a few examples:
- Tomcat + Derby + Jetspeed + ActiveMQ
- Jetty + Apache DS + ActiveMQ + OpenEJB
- Jetty + JOTM + Derby + OpenEJB
- Tomcat + ActiveMQ + Spring Kernel + ServiceMix
The Geronimo Kernel and GBeans make all of this possible. This is pretty cool IMO, especially with the whole Agile Java EE movement. Bruce thinks this is real future of Geronimo: the stacks that can be created with it. He expects the innovation and ideas in this area will come from the community and what users want.
Geronimo Community: Made up of many different open-source projects: MX4J, ActiveMQ, Tomcat, ActiveCluster, HOWL, JOTM, TranQL, Derby, Jetty, ServiceMix, OpenEJB. Rather than re-creating everything (the ol' NIH syndrome), the Geronimo team has tried to embrace and re-use other open source projects as much as possible. Many of the committers on the aforementioned projects are Geronimo committers or founders.
Bruce's favorite quote: In open source, we come for the code, we stay for the people.
Project Status: Now a top-level Apache project. Has officially passed J2EE 1.4 certification tests. The official 1.0 release date is "when it's done it's done", but the developers are hoping to finish by ApacheCon.