Which AWS service is used to "fan out" SQS messages to multiple queues?

Amazon Simple Notification Service (SNS) is the service designed to enable the "fan out" pattern for message delivery, allowing a single message to be sent to multiple destinations. When a message is published to an SNS topic, it can be delivered to multiple subscribers, which can include Amazon Simple Queue Service (SQS) queues, AWS Lambda functions, HTTP endpoints, and email addresses among others.

In this context, when you want to distribute or route messages across multiple SQS queues for processing, you publish the message to an SNS topic. Each SQS queue that is subscribed to this topic receives a copy of the message. This efficient mechanism avoids the need for the message producer to manually send the same message to each queue, thus effectively dividing the workload among them.

The ability to dynamically add or remove consumers (queues) to the SNS topic also adds to the flexibility, as it allows for easy scaling and adaptability based on changing requirements. This fan-out model fundamentally enhances the decoupling of systems and allows for robust message processing architectures in distributed applications.

Other options like S3, Lambda, and CloudWatch do not provide this specific functionality of fanning out messages to multiple SQS queues, which emphasizes the unique role of SNS in the AWS ecosystem.