Answer: Use Reserved Instances for the baseline level of usage. Use Spot Instances for any additional capacity that the application needs.

## Explanation **Correct Answer: B** **Why Option B is correct:** 1. **Reserved Instances for baseline usage**: The application has a predictable baseline load (moderate overnight usage and low weekend usage). Reserved Instances provide the lowest cost for predictable, steady-state workloads with a commitment of 1-3 years. 2. **Spot Instances for additional capacity**: During the 8-hour peak period each business day, the application needs additional capacity. Spot Instances offer up to 90% discount compared to On-Demand Instances and are suitable for stateless, fault-tolerant workloads that can handle interruptions. 3. **Cost optimization**: This combination minimizes costs while maintaining availability: - Reserved Instances ensure baseline capacity at the lowest cost - Spot Instances provide additional capacity during peaks at significant savings - The stateless nature of the application makes it suitable for Spot Instances **Why other options are incorrect:** **A. Use Spot Instances for the entire workload:** - Spot Instances can be interrupted with 2-minute notice - Using them for the entire workload would affect availability, especially for baseline overnight and weekend usage - Not suitable for production workloads that require guaranteed availability **C. Use On-Demand Instances for baseline, Spot for additional:** - On-Demand Instances are more expensive than Reserved Instances for baseline usage - This doesn't minimize costs as effectively as using Reserved Instances for baseline **D. Use Dedicated Instances for baseline, On-Demand for additional:** - Dedicated Instances are the most expensive option and provide physical isolation - This is not cost-optimized and is typically used for compliance/regulatory requirements - On-Demand for additional capacity is more expensive than using Spot Instances **Key AWS Concepts:** - **Reserved Instances**: Best for predictable workloads with steady-state usage - **Spot Instances**: Best for fault-tolerant, flexible workloads that can handle interruptions - **On-Demand Instances**: Pay-as-you-go with no commitment, most flexible but most expensive - **Dedicated Instances**: Physical isolation for compliance, most expensive option **Best Practice**: For production workloads with predictable baseline and variable peaks, use Reserved Instances for baseline and Spot Instances for peaks to achieve optimal cost savings while maintaining availability.

Author: LeetQuiz Editorial Team