Designing Fast Data Application Architectures

Chapter 3. The Message Backbone

The message backbone is a critical subsystem of a Fast Data platform that connects all its major components together. If you think about the message backbone as a nervous system, you can consider events as the triggers of electrical messages that travel back and forth across that system. The message backbone is the medium through which messages are sent and received from various sensors, data repositories, and data processors.

So what is an event?

An event can be defined as “a significant change in state.” For example, when a consumer purchases a car, the car’s state changes from “for sale” to “sold.” A car dealer’s system architecture may treat this state change as an event whose occurrence can be made known to other applications within the architecture. From a formal perspective, what is produced, published, propagated, detected, or consumed is a (typically asynchronous) message called the event notification, and not the event itself, which is the state change that triggered the message emission. Events do not travel; they just occur.

Event-driven architecture, Wikipedia

We can take away two important facts from this definition. The first is that event messages are generally asynchronous. The message is sent to signal observers that something has happened, but the source is not responsible for the way observers react to that information. This implies that the systems are decoupled from one another, which is an important property when building ...