Which AWS service or instance purchasing option should the company use to meet these requirements?

Explanations:

Spot Instances are ideal for workloads that are flexible and can tolerate interruptions, as they can be terminated by AWS when demand increases. They are not specifically designed to optimize usage based on predictable patterns of high and low demand, making them unsuitable for the company’s needs to manage instance count based on usage patterns.

Reserved Instances provide a significant discount over on-demand pricing but are intended for steady-state usage rather than variable workloads. They do not automatically adjust the number of instances based on usage patterns and require a commitment for a one- or three-year term, which does not align with the company’s fluctuating usage needs.

AWS CloudFormation is a service for automating the setup and deployment of AWS resources using code. While it can be used to manage EC2 instances, it does not directly optimize the number of instances based on usage patterns and does not offer automatic scaling capabilities.

AWS Auto Scaling automatically adjusts the number of EC2 instances based on the current demand and specified metrics (e.g., CPU utilization). This makes it suitable for optimizing usage during high-demand daytime hours and reducing capacity during lower-demand nighttime hours, effectively meeting the company’s requirements for cost-efficiency and performance.