Answer: Purchase a Capacity Reservation in the failover Region.

## Explanation **Correct Answer: D. Purchase a Capacity Reservation in the failover Region.** **Why this is correct:** 1. **Capacity Reservation** is specifically designed to guarantee EC2 capacity in a specific Availability Zone within a region. When designing a disaster recovery strategy, you need to ensure that when you fail over to the secondary region, you have guaranteed capacity available to launch your instances. 2. **Capacity Reservation vs Other Options:** - **On-Demand Instances (Option A):** While On-Demand instances provide flexible capacity, they don't guarantee availability. During a disaster scenario where many customers might be failing over to the same region, capacity could be limited. - **EC2 Savings Plan (Option B):** This provides cost savings but doesn't guarantee capacity. It's a pricing model, not a capacity guarantee. - **Regional Reserved Instances (Option C):** Regional RIs provide capacity discounts but only offer capacity priority, not guaranteed capacity. They can be applied across Availability Zones within a region but don't reserve specific capacity. 3. **Disaster Recovery Requirements:** For DR scenarios where you need to ensure you can launch instances in the failover region when needed, Capacity Reservation is the only option that provides actual capacity guarantees. **Key AWS Concepts:** - **Capacity Reservation:** Reserves capacity in a specific Availability Zone for any duration, ensuring you have EC2 capacity when you need it. - **Disaster Recovery Planning:** Requires guaranteed capacity in the failover region to ensure business continuity. - **Regional vs Zonal:** Capacity Reservation is zonal (specific AZ), while regional RIs provide flexibility across AZs but no capacity guarantee. **Best Practice:** For critical DR scenarios, use Capacity Reservations in the failover region to ensure you have the necessary EC2 capacity available when you need to execute your failover plan.

Author: LeetQuiz Editorial Team