Answer: A mix of On-Demand Instances and Spot Instances

## Explanation **Correct Answer: C - A mix of On-Demand Instances and Spot Instances** ### Why this is correct: 1. **Cost optimization without long-term commitment**: Spot Instances provide significant cost savings (up to 90% off On-Demand prices) without requiring any long-term commitment, unlike Reserved Instances which require 1- or 3-year commitments. 2. **Auto Scaling compatibility**: Spot Instances work well with Auto Scaling groups. When using a mixed instances policy, Auto Scaling can launch Spot Instances when capacity is available and fall back to On-Demand Instances when Spot capacity is unavailable. 3. **Fault-tolerant workload suitability**: Web applications that can handle interruptions (like those behind a load balancer) are ideal candidates for Spot Instances. If a Spot Instance is interrupted, Auto Scaling can automatically replace it with another instance. ### Why other options are incorrect: **A. Dedicated Instances only**: - Most expensive option - Provides physical isolation but no cost savings - Doesn't address the requirement for cost optimization **B. On-Demand Instances only**: - No cost savings compared to Spot Instances - Pay full price without any discounts - Doesn't optimize costs as requested **D. A mix of On-Demand Instances and Reserved Instances**: - Requires long-term commitment (1 or 3 years) - Violates the requirement of "without making a long-term commitment" - While it provides cost savings, it doesn't meet the no-commitment requirement ### Best Practice Implementation: For this scenario, the solutions architect should recommend: 1. **Mixed instances policy** in the Auto Scaling group 2. **Configure capacity rebalancing** to proactively replace Spot Instances that are at risk of interruption 3. **Use Spot Fleet** or **EC2 Auto Scaling with Spot integration** 4. **Set appropriate instance diversification** to use multiple instance types and Availability Zones 5. **Configure interruption handling** to gracefully handle Spot interruptions This approach maximizes cost savings while maintaining application availability and avoiding long-term commitments.

Author: LeetQuiz Editorial Team