Why Event-Driven Architecture?
Event-driven architecture (EDA) decouples systems, enables real-time data flow, and improves scalability. But it adds complexity - use it when the benefits outweigh the costs.
When EDA Makes Sense
Multiple systems need to react to the same business event
You need real-time data propagation (not batch)
Systems have different processing speeds (fast publishers, slow consumers)
You want to add new consumers without modifying producers
Message Broker Comparison
Apache Kafka - Distributed log for high-throughput, durable event streaming. Best for: event sourcing, data pipelines, high-volume systems.
RabbitMQ - Traditional message queue with flexible routing. Best for: task distribution, RPC patterns, moderate throughput.
AWS SQS/SNS - Managed messaging for AWS-centric architectures. Best for: serverless architectures, simple pub/sub, minimal operational overhead.
Saga Pattern
For distributed transactions across microservices, use the Saga pattern:
Choreography - Each service publishes events and reacts to events from others. Simple but hard to track end-to-end.
Orchestration - A central orchestrator coordinates the saga steps. More complex but easier to monitor and debug.
Event Sourcing
Store every state change as an immutable event rather than just the current state. Benefits: complete audit trail, temporal queries, easy debugging. Costs: increased storage, complexity in querying current state.
CQRS (Command Query Responsibility Segregation)
Separate read and write models. Writes go through commands to an event store. Reads come from projected views optimized for queries. Often combined with event sourcing.
Conclusion
Start with simple pub/sub messaging before adopting event sourcing or CQRS. Most enterprises benefit from EDA without the full complexity of event sourcing.