AWS Certified Solutions Architect – Professional (SAP-C02) — Question 20

A company uses an on-premises data analytics platform. The system is highly available in a fully redundant configuration across 12 servers in the company’s data center.
The system runs scheduled jobs, both hourly and daily, in addition to one-time requests from users. Scheduled jobs can take between 20 minutes and 2 hours to finish running and have tight SLAs. The scheduled jobs account for 65% of the system usage. User jobs typically finish running in less than 5 minutes and have no SLA. The user jobs account for 35% of system usage. During system failures, scheduled jobs must continue to meet SLAs. However, user jobs can be delayed.
A solutions architect needs to move the system to Amazon EC2 instances and adopt a consumption-based model to reduce costs with no long-term commitments. The solution must maintain high availability and must not affect the SLAs.
Which solution will meet these requirements MOST cost-effectively?

Answer options

• A. Split the 12 instances across two Availability Zones in the chosen AWS Region. Run two instances in each Availability Zone as On-Demand Instances with Capacity Reservations. Run four instances in each Availability Zone as Spot Instances.
• B. Split the 12 instances across three Availability Zones in the chosen AWS Region. In one of the Availability Zones, run all four instances as On-Demand Instances with Capacity Reservations. Run the remaining instances as Spot Instances.
• C. Split the 12 instances across three Availability Zones in the chosen AWS Region. Run two instances in each Availability Zone as On-Demand Instances with a Savings Plan. Run two instances in each Availability Zone as Spot Instances.
• D. Split the 12 instances across three Availability Zones in the chosen AWS Region. Run three instances in each Availability Zone as On-Demand Instances with Capacity Reservations. Run one instance in each Availability Zone as a Spot Instance.

Correct answer: D

Explanation

Option D ensures high availability by spreading the instances across three Availability Zones, maintaining redundancy with three On-Demand Instances and one Spot Instance per zone. This configuration allows for meeting the tight SLAs of scheduled jobs while also being cost-effective by incorporating Spot Instances. The other options either do not provide enough On-Demand Instances to maintain SLAs or do not optimize the cost structure effectively.