A data file should arrive in an S3 bucket every hour. An S3 event triggers a Lambda function to process each arrival. Occasionally a file does not arrive, and the application team wants to be alerted when no file is received during an hour. Which solution is the most operationally efficient and satisfies this requirement?

The most operationally efficient solution is to monitor the Lambda function's Invocations metric. If no file arrives, the S3 event will not trigger the Lambda function, resulting in zero invocations. A CloudWatch alarm configured to treat missing data as a breach for this metric over an hour will accurately detect the absence of a file and alert via SNS. Incorrect options: An S3 lifecycle rule is designed for object transitions or expirations, not for detecting the absence of new objects. It cannot trigger based on zero objects being transitioned. An S3 event invoking a Lambda function that posts to an SQS queue would only occur if a file does arrive. If no file arrives, no message is sent to SQS, and the ApproximateAgeOfOldestMessage metric would not be useful for detecting missing files. A Lambda function scheduled hourly to check the newest object's timestamp would work but is less efficient. It requires maintaining and executing an additional Lambda function and an EventBridge rule, whereas monitoring the existing Lambda's invocation metric is a simpler, built-in CloudWatch capability.