In what scenario would you use SNS?

Using Amazon Simple Notification Service (SNS) is ideal for sending notifications to multiple subscribers. SNS is designed specifically for message delivery and notification purposes, allowing one message to be broadcast to multiple endpoints, such as Lambda functions, HTTP/S endpoints, emails, and SMS. This capability makes it powerful for applications that need to alert users, automate responses, or distribute real-time messages efficiently across various channels.

In scenarios where you need to ensure that updates or notifications reach multiple recipients simultaneously—such as alerting system administrators of an application failure or informing users of important updates—SNS is an excellent choice. It can simplify the communication process and reduce the complexity of managing messages across different formats and transport mechanisms.

Other options involve functionalities that fall outside the primary capabilities of SNS. For instance, storing documents in S3 pertains to object storage, managing database transactions relates to database services like DynamoDB or RDS, and creating a new EC2 instance involves AWS infrastructure services. None of these operations utilize the notification delivery mechanism that SNS is built for, further reinforcing why sending notifications to multiple subscribers is the appropriate use case for SNS.