A web application runs on EC2 instances in a single AWS Region and must remain fully available and perform without degradation even if one Availability Zone fails. The application requires at least 12 instances in total at all times. Which deployment uses the fewest running instances while meeting those requirements?

The requirement is for 12 instances to be available at all times, even if an Availability Zone (AZ) fails. If one AZ fails, its instances become unavailable. To maintain 12 instances, the remaining AZs must collectively host at least 12 instances. Option 4 (3 AZs with 6 instances each) provides a total of 18 instances. If one AZ fails, 12 instances remain (6 + 6), meeting the requirement with the fewest running instances among the viable options. Option 1 (2 AZs with 6 instances each) provides 12 instances. If one AZ fails, only 6 instances remain, which is insufficient. Option 2 (2 AZs with 12 instances each) provides 24 instances. If one AZ fails, 12 instances remain, meeting the requirement but using more instances than necessary (24 vs. 18). Option 3 (3 AZs with 4 instances each) provides 12 instances. If one AZ fails, only 8 instances remain, which is insufficient.