AWS Certified Solutions Architect - Associate

Explanation

Correct Answer: D - Create an On-Demand Capacity Reservation that specifies the Region and three Availability Zones needed.

Why Option D is Correct:

1. On-Demand Capacity Reservations are specifically designed to guarantee EC2 capacity in a specific Availability Zone for a specific duration.
2. The requirement is for guaranteed capacity in three specific Availability Zones for a 1-week event.
3. Capacity Reservations allow you to reserve capacity in specific AZs, ensuring you have access to EC2 instances when needed.
4. You can create multiple Capacity Reservations across different AZs to meet the requirement.

Why Other Options are Incorrect:

Option A & C (Reserved Instances):

• Reserved Instances provide cost savings but do NOT guarantee capacity.
• They are a billing discount applied to running instances, not a capacity guarantee.
• Even with Reserved Instances, you might not get capacity if the AZ is at full capacity.

Option B:

• Creating an On-Demand Capacity Reservation that specifies only the Region is insufficient.
• Capacity Reservations must be created for specific Availability Zones to guarantee capacity in those zones.
• Regional reservations don't guarantee capacity in specific AZs.

Key AWS Concepts:

• Capacity Reservations: Guarantee capacity in specific AZs for On-Demand Instances
• Reserved Instances: Provide cost savings but no capacity guarantee
• Duration: Capacity Reservations can be created for any duration and are billed by the second
• Flexibility: You can cancel Capacity Reservations at any time (with some billing implications)

Best Practice:

For time-sensitive events requiring guaranteed capacity in specific AZs, always use On-Demand Capacity Reservations rather than relying on Reserved Instances.