Event-driven serverless core for B2B SaaS

The problem

A growing B2B SaaS had stuffed everything into synchronous API handlers. Long-running work blocked requests, retries were ad hoc, and a single slow downstream service degraded the whole product. There was no clean way to add new consumers without touching the request path.

The solution

Modeled the domain as events first. Commands hit a thin Lambda API, which writes to DynamoDB and emits domain events to EventBridge. Bounded contexts subscribe with their own Lambda consumers, retry with SQS, and dead-letter to a triage queue with replay tooling. Step Functions orchestrate multi-step workflows that need durability. Each event has a versioned schema in the registry.

Architecture

Stack

Outcomes