Which feature of S3 allows users to automate workflows based on bucket changes?

S3 Event Notifications are the feature of Amazon S3 that allow users to automate workflows based on changes made to objects in a bucket. When certain events occur—such as object creation, deletion, or updates—S3 can trigger notifications that can be sent to various services like Lambda functions, SNS (Simple Notification Service), or SQS (Simple Queue Service). This capability enables seamless integration with other AWS services, allowing developers to create automated processing pipelines or workflows in response to specific actions on the S3 bucket.

For instance, when an object is uploaded to a specific S3 bucket, an event notification can be used to trigger a Lambda function that processes the file, moves it to another bucket, or performs other tasks. This automation is a key feature in developing responsive and efficient cloud architectures.

The other options do not provide this specific functionality. S3 Lifecycle Rules are used to manage the lifecycle of objects in the bucket, including transitioning them between storage classes or expiring them after a defined period. S3 Select allows users to retrieve a subset of data from within an object, which is useful for querying large datasets without retrieving the entire object. S3 Default Encryption is a security feature that ensures that all objects stored in a bucket are encrypted by default,