Which EC2 instance purchasing option is MOST cost-effective for this use case?

Explanations:

Reserved Instances are cost-effective for applications with steady-state usage. However, since the application is idle for months, paying for reserved capacity during those periods is not economical.

Spot Instances offer significant cost savings by allowing users to bid on unused EC2 capacity. Since the application can handle interruptions gracefully and is idle for long periods, this option is the most cost-effective for processing large volumes of data when needed.

Dedicated Instances provide physical isolation on hardware, which is unnecessary for this use case and incurs higher costs. This is not suitable given the application’s intermittent workload and idleness.

On-Demand Instances are flexible but can become expensive over time, especially if the application remains idle for months. This option does not provide the cost savings that Spot Instances offer for sporadic usage.