A company runs a custom report program to analyze mobile app usage. The program generates multiple reports during the last week of each month; each report takes less than 10 minutes. The program is rarely used outside that last week. The company wants to produce reports as quickly as requested at the MOST cost-effective price. Which solution meets these requirements?

The correct solution is to run the program in AWS Lambda and use an Amazon EventBridge rule to invoke the Lambda function when reports are requested. This is the most cost-effective and efficient approach for an infrequently used, short-duration task. Lambda is serverless, meaning you only pay for the compute time consumed, which aligns perfectly with the "rarely used" and "less than 10 minutes" requirements. EventBridge provides a simple way to trigger the function on demand. Running on EC2 On-Demand or Spot Instances would incur costs for the instance uptime, even if the program is idle, which is not cost-effective for a task used only during the last week of the month. Spot Instances also carry the risk of interruption, which is undesirable for report generation. Amazon ECS would also involve managing containers and underlying infrastructure, adding complexity and potential cost compared to the fully managed Lambda service for this specific use case.