Which AWS service will support this application MOST cost-effectively?

Explanations:

Amazon ECS is designed for running containerized applications. While it can handle applications with infrequent invocations, it typically incurs costs related to running the service continuously, making it less cost-effective for an application with low usage and short processing times.

AWS Lambda is a serverless compute service that automatically scales and charges only for the time your code runs, making it highly cost-effective for applications that are invoked infrequently and have short processing durations (less than 5 minutes).

Amazon EKS is a managed Kubernetes service, which is suited for applications requiring orchestration of multiple containers. It generally involves higher operational costs and complexity compared to AWS Lambda, making it less ideal for a simple, infrequently invoked application.

Amazon EC2 provides virtual servers in the cloud and would require provisioning resources that would run continuously, leading to unnecessary costs for an application that is only invoked a few times daily with quick processing times.