A Solutions Architect is designing a web tier that must survive the failure of an entire Availability Zone with no manual intervention. Which combination of services should be used?
A) A single EC2 instance with an Elastic IP, manually moved to a new AZ if a failure occurs.
B) An Application Load Balancer distributing traffic across an Auto Scaling Group spanning at least two AZs.
C) An Application Load Balancer with EC2 instances in a single AZ behind it.
D) Amazon Route 53 simple routing pointing to a single EC2 instance.
Correct Answer: B
Explanation: An Auto Scaling Group spanning multiple AZs, fronted by an Application Load Balancer, automatically routes traffic only to healthy instances and can launch replacement instances in a surviving AZ if one AZ fails — achieving high availability without manual intervention.
Why the others are wrong: (A) requires manual action and has no redundancy. (C) still has a single point of failure: if that one AZ goes down, the entire application becomes unavailable. (D) has no automatic failover or health-check-based routing.