How to fan out events with Amazon SNS

Amazon SNS is a managed publish/subscribe service. A publisher sends a message to a topic and SNS delivers a copy to every subscriber, queues, Lambda functions, HTTP endpoints, or email. The classic pattern is SNS-to-SQS fan-out: one event drives several independent processors, each with its own buffered queue.

Prerequisites

• An AWS account and the AWS CLI.
• One or more SQS queues to receive events.

Steps

1. Create a topic

aws sns create-topic --name order-events

2. Subscribe queues

aws sns subscribe --topic-arn <topic-arn> --protocol sqs --notification-endpoint <queue-arn>

Enable raw message delivery so consumers receive the bare payload, not the SNS envelope.

3. Subscribe a Lambda

aws sns subscribe --topic-arn <topic-arn> --protocol lambda --notification-endpoint <function-arn>

Grant SNS permission to invoke the function with aws lambda add-permission.

4. Publish an event

aws sns publish --topic-arn <topic-arn> --message '{"orderId":1,"type":"created"}'

Every subscriber receives a copy.

5. Add a filter policy

Subscriptions can filter on message attributes so each subscriber sees only relevant events:

{ "type": ["created"] }

Attach this as the subscription's FilterPolicy to skip irrelevant messages without delivering them.

6. Set the queue policy

Each subscribed queue needs a policy allowing the SNS topic to send messages to it. Without it, deliveries silently fail.

Verification

Publish one event and confirm a message lands in every subscribed queue and the Lambda fires. Add a filter policy, publish a non-matching event, and confirm only matching subscribers receive it. Check the topic's CloudWatch NumberOfNotificationsDelivered metric.

Next Steps

Use a dead-letter queue on subscriptions for failed deliveries, encrypt the topic with KMS, and evaluate EventBridge when you need richer routing rules.