Event-driven architecture (EDA) decouples systems through asynchronous events. Instead of direct calls between services, components publish and subscribe to events. This creates flexible, scalable systems that handle change gracefully.
Core Concepts#
Events vs Commands vs Queries#
Event:
- Something that happened (past tense)
- "OrderPlaced", "UserRegistered", "PaymentProcessed"
- Immutable fact
- Multiple consumers possible
Command:
- Request to do something (imperative)
- "PlaceOrder", "RegisterUser", "ProcessPayment"
- Single handler
- May be rejected
Query:
- Request for information
- "GetOrder", "FindUser", "ListPayments"
- Returns data
- No side effects
Event Structure#
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Event Patterns#
Publish-Subscribe#
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Event Sourcing#
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CQRS (Command Query Responsibility Segregation)#
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Message Brokers#
Redis Streams#
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RabbitMQ#
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Error Handling#
Dead Letter Queues#
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Idempotency#
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Testing Event-Driven Systems#
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Best Practices#
Event Design#
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Event Versioning#
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Conclusion#
Event-driven architecture enables scalable, loosely-coupled systems. Events capture what happened, subscribers react independently, and the system evolves without tight dependencies.
Start simple—basic pub/sub covers most needs. Add event sourcing and CQRS when you need audit trails or complex read models. The key is designing meaningful events that capture business reality.