AWS Certified SysOps Administrator – Associate — Question 312

A company's web application runs on Amazon EC2 instances in a single AWS Region. The infrastructure must be designed so the application remains available with no performance degradation in the event of an Availability Zone (AZ) failure. To ensure optimal performance, the application must maintain a minimum of 12 instances at all times.

Which solution will meet the requirements with the fewest running instances possible?

Answer options

• A. 2 AZs with 6 instances in each AZ
• B. 2 AZs with 12 instances in each AZ
• C. 3 AZs with 4 instances in each AZ
• D. 3 AZs with 6 instances in each AZ

Correct answer: D

Explanation

To maintain a minimum of 12 Amazon EC2 instances during an Availability Zone (AZ) failure, the remaining zones must collectively host at least 12 active instances. Option D (3 AZs with 6 instances each, totaling 18) satisfies this requirement because if one AZ fails, the remaining two AZs will still have exactly 12 running instances, which uses fewer instances than Option B's total of 24. Options A and C are incorrect because an AZ outage would leave only 6 and 8 instances respectively, failing to meet the minimum requirement of 12.