SNS Fan-Out Pattern with SQS

The SNS fan-out pattern is one of the most important architectural patterns in AWS event-driven systems. By combining SNS topics with SQS queues, you can broadcast a single event to multiple independent consumers, each processing the event at its own pace with its own retry logic and dead-letter queue.

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What Is Fan-Out?

Fan-out means taking a single input and distributing it to multiple outputs. In the context of messaging:

• A producer publishes one message to an SNS topic
• The SNS topic delivers a copy of that message to multiple SQS queues
• Each SQS queue has its own independent consumer

                              +——> [SQS: email-queue]    ——> Email Service
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Producer ——> [SNS Topic] ——>  +——> [SQS: analytics-queue] ——> Analytics Service
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                              +——> [SQS: inventory-queue] ——> Inventory Service

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Why SNS + SQS? Why Not SNS Alone?

SNS pushes messages to subscribers immediately. If the subscriber is unavailable or slow, the message may be lost (for some subscriber types) or create backpressure. Adding SQS queues as subscribers provides: