Building Event-Driven Microservices

Chapter 2. Event-Driven Microservice Fundamentals

An event-driven microservice is a small application built to fulfill a specific bounded context. Consumer microservices consume and process events from one or more input event streams, whereas producer microservices produce events to event streams for other services to consume. It is common for an event-driven microservice to be a consumer of one set of input event streams and a producer of another set of output event streams. These services may be stateless (see Chapter 5) or stateful (see Chapter 7) and may also contain synchronous request-response APIs (see Chapter 13). These services all share the common functionality of consuming events from or producing events to the event broker. Communication between event-driven microservices is completely asynchronous.

Event streams are served by an event broker, which is covered in more detail in the second half of this chapter. Running microservices at any meaningful scale often necessitates using deployment pipelines and container management systems, also discussed near the end of this chapter.

Building Topologies

The term topology comes up frequently in discussions of event-driven microservices. This term is often used to mean the processing logic of an individual microservice. It may also be used to refer to the graph-like relationship between individual microservices, event streams, and request-response APIs. Let’s look at each definition in turn.

Microservice Topology

A microservice ...