Agile Architecture

Agile (or eXtreme Programming) development usually focuses on the development of the software itself, but it can (and should) be applied to all parts of the system. If the architecture of the system is determined before the first iteration and not open for refactoring or other redesign principles, then it falls into the category of BigDesignUpFront. To put the problem another way, how can the domain of the system be determined if what the system will do is not determined? And, if the system functionality is already determined, then there's no room to DoTheSimplestThingThatCouldPossiblyWork.

One argument against DoTheSimplestThingThatCouldPossiblyWork is that nothing complex (like a compiler) would be built. I disagree, simply because DTSTTCPW should only be applied to the domain as it is understood. So TheSimplestThing when you are getting started should be different than TheSimplestThing as your system becomes operational. TheSimplestThing when you are working in isolation on your personal computer becomes massively different from TheSimplestThing when you are providing a service on the Internet. As a ridiculous example, think about the problem of searching for a given word in your filesystem. Would you build Google to do it? No (or I sincerely hope not). You'd use find or perl or some other script language. Now, if you want to let anyone search for any word in any word on the Internet, now you've got to build Google, and all the system availability and performance benchmarks that go along with it.

The great thing about Web technologies is that they scale well, and don't require replacing to service greater demand or performance objectives. If one webserver can handle your own requests, then a cluster can handle thousands of them. But how do you refactor an architecture? Most people think of architecture as an inflexible part of the design. Nothing could be further from the truth. Writing POJOs (Plain Old Java Objects) leads quickly into EJBs (Enterprise Java Beans) in a J2EE container, or web services. Same goes for any web-based scripting language. Command line PHP can be easily hosted by Apache and serve the same data over the web.

The key point is that just as your software should be designed iteratively, so should the archtiecture. As the system requirements grow and change, the architecture should grow and change with it. Will there be additional software changes to handle the new architecture? Probably. Will the overall system be better suited to handle the system parameters? Yes. Otherwise, you will be trying to put a now square peg into a hole that's still round. It can be done, but is sure isn't TheSimplestThing.