There isn't much said in typical Agile conversation about architecture and modularity. We will attempt to redress this omission by examining an agile approach to logical system architecture coupled with a potential implementation for the Java platform.

Tracer Bullet Development (TBD) is a technique that allows you to prove out the proposed architecture of your system by firing a "tracer bullet" through a vertical slice of your system that exercises all of its horizontal components. It has multiple benefits, including encapsulation, decoupled code, parallel code development, and more.

OSGi is a specification for a dynamic module system for Java with multiple open source implementations. It allows you to modularize your system into "bundles" which essentially firewall their own classloader space. Objects running within a bundle can only see types that they explicitly import and only expose types that they explicitly export. They interact with other bundles by expose and consuming services which are registered under a public interface.

At face value it seems that Tracer Bullet Development and OSGi are a match made in heaven!

In this talk, we'll examine the principles undergirding TBD, the pros and cons of this approach, and walk through the design of a system using TBD. We'll also get a brief introduction to OSGi and its various implementations, look at some of the tools available for OSGi development, and then implement our TBD design.