Building Event-Driven Microservices

Chapter 3. Communication and Data Contracts

The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point.

Claude Shannon

Shannon, known as the Father of Information Theory, identified the largest hurdle of communication: ensuring that a consumer of a message can accurately reproduce the producer’s message, such that both the content and meaning are correctly conveyed. The producer and consumer must have a common understanding of the message; otherwise, it may be misinterpreted, and the communication will be incomplete. In the event-driven ecosystem, the event is the message and the fundamental unit of communication. An event must describe as accurately as possible what happened and why. It is a statement of fact and, when combined with all the other events in a system, provides a complete history of what has happened.

Event-Driven Data Contracts

The format of the data to be communicated and the logic under which it is created form the data contract. This contract is followed by both the producer and the consumer of the event data. It gives the event meaning and form beyond the context in which it is produced and extends the usability of the data to consumer applications.

There are two components of a well-defined data contract. First is the data definition, or what will be produced (i.e., the fields, types, and various data structures). The second component is the triggering logic, or why it ...