An ecommerce app needs to call three independent third-party systems concurrently when a sale occurs. You implemented three separate Lambda functions (one per third party) and want each to run regardless of the others' success or failure. Which design satisfies this requirement?

Publishing the sale event to an Amazon SNS topic and subscribing the three Lambda functions to it is the correct solution. SNS is a publish/subscribe service that allows multiple subscribers to receive the same message concurrently. Each Lambda function will be invoked independently when a message is published to the topic, satisfying the requirement that they run regardless of each other's success or failure. Using an SQS queue with polling Lambdas would require complex logic to ensure each Lambda processes the same message, as SQS is designed for single-consumer processing. Sending to an ALB with Lambda targets is not suitable for asynchronous, independent invocations; ALB is for synchronous HTTP requests. AWS Step Functions could orchestrate this, but the question specifies independent execution, and moving logic into the state machine is an unnecessary refactor given the independent nature of the calls.