Event-driven architecture decouples components by communicating through events. Publishers emit events without knowing who listens. Subscribers react without knowing who published.
Node.js EventEmitter
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Application Event Bus
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Domain Events
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Message Queue Integration
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Event Sourcing
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CQRS Pattern
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Saga Pattern
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Best Practices
Event Design:
✓ Use past tense (OrderPlaced, not PlaceOrder)
✓ Include all relevant data
✓ Make events immutable
✓ Version your events
Implementation:
✓ Handle failures gracefully
✓ Make handlers idempotent
✓ Use transactions for consistency
✓ Monitor event processing
Avoid:
✗ Circular event chains
✗ Business logic in handlers
✗ Blocking event processing
✗ Losing events on failure
Conclusion
Event-driven architecture enables loose coupling and scalability. Start with in-process events, graduate to message queues as needed, and consider event sourcing for audit trails and complex domains.