/aws/sns
A pub/sub broadcast channel. Publish once to a topic; every subscriber gets a copy — SQS queues, Lambdas, HTTPS endpoints, email, SMS, mobile push. No retention: if nobody's subscribed, the message is gone. The default answer for "one event, many independent reactions," almost always paired with per-consumer SQS queues for durability.
Both make your system asynchronous, but they solve different problems. Queue semantics vs topic semantics, when to reach for each, and the SNS → SQS fan-out pattern that shows up in real system designs.
Build the SNS-to-SQS fan-out pattern where each consumer owns a private queue with its own retry policy and DLQ. Covers queue policies, raw message delivery, redrive config, and the delivery guarantees you actually get.