dabydat/alpha-omega/nestjs-event-driven-architecture

NestJS Event-Driven Architecture (EDA)

EDA is a communication pattern where services communicate via asynchronous events rather than synchronous calls. Events enable loose coupling, scalability, and resilience.

Why Event-Driven Architecture

See references/why-eda.md for the ❌ BAD synchronous-call example and the ✅ GOOD event-driven example.

Event Anatomy

Domain Events

See references/domain-events.md for UserCreatedEvent and MerchantAdminUserCreatedEvent.

Event Message Format

See references/domain-events.md for UserCreatedMessage.

Event Publishing

Publishing from Aggregate

See references/event-publishing.md (aggregate calls this.apply(...)).

Event Publisher Port (Hexagonal)

See references/event-publishing.md (EVENT_PUBLISHER_PORT interface).

Adapter Implementation

See references/event-publishing.md (EventPublisherAdapter).

Event Consumers

Consumer Service Pattern

See references/event-consumers.md (UserEventConsumerService).

Cross-Service Event Consumption

See references/event-consumers.md (AuthenticationEventConsumerService).

Event Handlers (CQRS Event Handlers)

@EventsHandler Pattern

See references/event-handlers.md (UserUpdatedHandler).

Topic Constants

See references/topic-constants.md (TopicConstant).

Consumer Groups

See references/topic-constants.md (KafkaGroupsConstant).

Event Flow Example

See references/event-flow.md for the user-service → Kafka → merchant-service sequence.

Retry Configuration

See references/retry-config.md.

Anti-Patterns to Avoid

See references/anti-patterns.md for the four ❌ examples (with fixes).

Summary: EDA Responsibilities

Golden rule: Services communicate via events, not direct calls. Events are contracts — design them carefully and version them.