Event-Driven Architecture (EDA) Design Patterns

EDA is a design paradigm in which components communicate by producing and reacting to events, state changes that are published to a broker or log, rather than through direct calls.

Instead of storing only current state, the system stores the sequence of events that led to it; state is rebuilt by replaying them, which gives a full audit trail.

Command Query Responsibility Segregation separates the model used to change data from the model used to read it, so each can be optimised and scaled independently.

A saga coordinates a business transaction across several services as a sequence of local transactions with compensating actions, instead of a distributed transaction.

It writes the event to an outbox table in the same database transaction as the state change, so the event is published reliably without dual writes.