On Microservices and Event-Driven Architectures

I recently participated in a software architecture conference, in which the two leading sessions were “microservices architecture” and “event driven architecture.”

Microservices architecture gained momentum in recent year as a way to break the monolithic database architecture into small independent units that are decoupled and independent. Each unit has its own database, which deviates from the principle of a monolithic normalized database within the enterprise. Microservices is a derivative of the “Service Oriented Architecture” and adds the decoupling principle.

Event-driven architectures have evolved over the last two decades in conjunction with event-driven systems. These architectures follow the agent paradigm in which the basic components are producers, consumers and event-processing agents (in the middle of the drawing).In the above architecture, the event-processing agents receive one or more events from producers, which could be IoT sensors, applications, or business processes. The event agents perform some processing (filtering, aggregation, pattern detection), and emit one or more events. The architecture is decoupled; thus an agent does not have any binding to any other agent, producer, or consumer. As such there is a similarity to the microservices architecture.

The differences are that microservices architecture is not necessarily event driven. While in event-driven architecture, an agent is activated by the arrival of an event, in microservices architecture an event can be activated by an explicit call. For instance, if I want to calculate the balance of my bank account, I am calling a service that does this calculation and shows me the result (or just brings it from a database). In contrast, in event-driven architecture, the different functions are not explicitly called but triggered by the occurrence of a specific event (e.g. in connected cars. the velocity exceeds the speed limit).

In event-driven architectures, each agent owns its internal state, but databases are external entities that are not necessarily associated with a single agent.

Since enterprise applications will be blend of event-driven, data-driven and process-driven software units, the decoupling principle provides the possibility to do an overall enterprise architecture based on unified principles.

Related: On error handling as event processing

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