Event-Driven Architecture Modernization — AWS Solutions Architect (SAA-C03)
Fan-out, ordering, and routing needs separate the services
Architecture requirement: decouple application components so they respond to state changes independently. Competing choices: SQS (queue, one consumer per message), SNS (topic, fan-out to multiple subscribers), EventBridge (event bus, rule-based conditional routing), Kinesis (ordered stream, replay capable). Deciding constraint: does the event require fan-out, ordering guarantees, replay capability, or conditional routing logic? SQS for point-to-point; SNS for fan-out; EventBridge for conditional routing; Kinesis for ordered, replayable streams. These are architecturally distinct — selecting by vague category is how distractors succeed.
What This Pattern Tests
The exam presents a tightly coupled system and asks how to decouple with events. SQS is for point-to-point: one producer, one consumer, messages buffered until processed (order processing, task queues). SNS is for fan-out: one event triggers multiple subscribers in parallel (email + SMS + Lambda). EventBridge is for content-based routing: events from 35+ AWS sources routed to targets based on event content (only route "order.placed" events to the billing service, "order.shipped" to the notification service). The trap is using SQS when multiple consumers need the same event (use SNS+SQS fan-out pattern) or EventBridge for simple point-to-point buffering (SQS is simpler and cheaper).
Decision Axis
Communication pattern determines the service: point-to-point buffering = SQS, parallel fan-out = SNS, content-based routing = EventBridge, fan-out with buffering = SNS+SQS.
Associated Traps
More Top Traps on This Exam
Decision Rules
When exactly one downstream consumer must process each message with buffering and retention guarantees, SQS is the correct point-to-point primitive; SNS is disqualified because its push-based fan-out model provides no message buffering and is not designed for single-consumer delivery.
Domain Coverage
Difficulty Breakdown