A company runs a stateless web application in production on Amazon EC2 On-Demand Instances behind an Application Load Balancer. Usage is heavy for 8 hours each business day, moderate and steady overnight, and low on weekends. The company wants to minimize EC2 costs while maintaining availability. Which approach meets these requirements?

The correct approach uses Reserved Instances (RIs) for the predictable, steady-state workload and Spot Instances for the fluctuating, additional capacity. RIs offer significant cost savings (up to 72% compared to On-Demand) for a committed usage period, making them ideal for the consistent overnight and weekend baseline. Spot Instances provide even greater savings (up to 90% off On-Demand) but can be interrupted, making them suitable for stateless, fault-tolerant workloads that can tolerate interruptions, like the peak daily usage. Using Spot Instances for the entire workload is too risky due to potential interruptions, which would impact availability during critical periods. Using On-Demand Instances for the baseline is more expensive than RIs. Dedicated Instances are for specific compliance or licensing needs and are the most expensive option, not primarily for cost optimization.