Building Event-Driven Microservices with NestJS and AWS SNS/SQS
Event-driven architecture is a powerful pattern for building scalable, loosely coupled systems. In this post, I'll walk you through how I architected a global payroll SaaS with 8 event-driven microservices at Collectwire.
Why Event-Driven Architecture?
Traditional REST-based microservices create tight coupling between services. When Service A calls Service B synchronously, a failure in B cascades to A. Event-driven architecture breaks this coupling using a message broker as an intermediary.
Setting Up AWS SNS and SQS
AWS SNS (Simple Notification Service) acts as the event publisher, while SQS (Simple Queue Service) provides durable, at-least-once delivery guarantees.
Implementing the Saga Pattern
For distributed transactions spanning multiple services, we use the Saga pattern — a sequence of local transactions where each step publishes events to trigger the next.
Key Takeaways
- Idempotency is critical: Design your event handlers to be idempotent
- Dead Letter Queues: Always configure DLQs for failed message handling
- Observability: Correlate events with trace IDs across services
- Schema Registry: Use a schema registry to manage event contracts
The result? 99.9% uptime, 3× delivery velocity, and infrastructure that scales effortlessly.
