Event-Driven Architecture (EDA)

What is an event?
Components
Patterns
Advantages
Challenges
Use cases
Examples

Event-Driven Architecture (EDA) is about using events as a way to communicate within a system. Generally, leveraging a message broker to publish and consume events asynchronously. The publisher is unaware of who is consuming an event and the consumers are unaware of each other. Event-Driven Architecture is simply a way of achieving loose coupling between services within a system.

What is an event?

An event is a data point that represents state changes in a system. It doesn't specify what should happen and how the change should modify the system, it only notifies the system of a particular state change. When a user makes an action, they trigger an event.

Components

Event-driven architectures have three key components:

Event producers: Publishes an event to the router.
Event routers: Filters and pushes the events to consumers.
Event consumers: Uses events to reflect changes in the system.

Note: Dots in the diagram represents different events in the system.

Patterns

There are several ways to implement the event-driven architecture, and which method we use depends on the use case but here are some common examples:

Note: Each of these methods is discussed separately.

Advantages

Let's discuss some advantages:

Decoupled producers and consumers.
Highly scalable and distributed.
Easy to add new consumers.
Improves agility.

Challenges

Here are some challenges of event-drive architecture:

Guaranteed delivery.
Error handling is difficult.
Event-driven systems are complex in general.
Exactly once, in-order processing of events.

Use cases

Below are some common use cases where event-driven architectures are beneficial:

Metadata and metrics.
Server and security logs.
Integrating heterogeneous systems.
Fanout and parallel processing.

Examples

Here are some widely used technologies for implementing event-driven architectures:

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