It’s been 15 years since the dawn of the Web, and we are still absorbing the lessons it teaches us about decentralization, loose coupling, standards, and resource representation. Even when technology seems to move quickly, it can take a long time to understand, appreciate, and apply the core principles it embodies.

The roots of event-driven architecture run even deeper. Twenty-five years ago, the graphical user interface forever changed how we think about applications. Suddenly, the event loop became a central organizing principle. Programs listened to events, processed them, and responded to them—sometimes by firing new events. There was no other way to effectively support fickle and unpredictable users who are liable to do anything whenever they want.

Enterprise software systems, of course, serve whole populations of fickle and unpredictable users. Some are customers, some are suppliers, and some are business partners. Here too, effective software has to listen well and respond intelligently.

It sounds simple, and conceptually it is. But while the stream of events produced by a GUI application is defined by the operating system, and is well understood by the programmer, an enterprise application lives in a connected world. Just as the resource-oriented Web architect has to learn how to design stateless resources, so must the event-oriented enterprise architect learn how to design stateless events.

But if EDA presents new challenges, it also emerges in an era of new opportunity. The tools and techniques of service-oriented architecture are becoming more mature, more interoperable, and more manageable.

With a strong SOA skeleton in place, EDA can weave the enterprise’s nervous system. This book explains why event-driven architecture yields smart and resilient enterprise software, and shows you how to start “thinking EDA.”

—Jon Udell