Users upload documents to an S3 bucket through a web UI. An S3 event triggers a Lambda function to process each upload, but the Lambda sometimes times out. With the Lambda configured using default settings, what happens to the S3 event when the function times out?

When an S3 event notification triggers a Lambda function and the function times out, S3's default behavior is to retry the delivery of the event. S3 will attempt to deliver the event up to three times in total (the initial attempt plus two retries). If the Lambda function still times out after these retries, the S3 event notification is discarded. Amazon SNS is not involved by default for Lambda timeouts. The event is not sent to a default Dead Letter Queue (DLQ) unless one is explicitly configured for the Lambda function. S3 does not continue retrying indefinitely; it has a fixed retry policy for event notifications.