What should the solutions architect recommend?

Explanations:

EC2 Spot Instances are ideal for highly dynamic, stateless workloads that can be interrupted and can significantly reduce costs compared to On-Demand Instances. Given that the job can be started and stopped at any time, using Spot Instances allows the company to take advantage of lower prices while handling variable workloads efficiently.

EC2 Reserved Instances are not cost-effective for a highly dynamic job that can start and stop at any time, as they require a commitment to a specific instance type and region for a one- or three-year term. This approach would lead to unnecessary costs since the job’s stateless nature does not guarantee continuous usage of the reserved capacity.

EC2 On-Demand Instances provide flexibility and are billed by the hour, but they are more expensive than Spot Instances for batch processing jobs. In this scenario, where cost-effectiveness is crucial and the workload is dynamic, On-Demand Instances would not be the best option.

AWS Lambda is suitable for short-lived, stateless functions but is limited by a maximum execution time of 15 minutes. Since the processing job typically takes upwards of 60 minutes to complete, Lambda would not be appropriate for this use case, making this option incorrect.