A web tier runs on a single EC2 instance in one Availability Zone. The company needs the application to keep serving requests if that AZ fails. What is the simplest resilient redesign?
A.Move the instance to a larger instance type
Vertical scaling does not survive an AZ failure.
B.Place an Application Load Balancer in front of an Auto Scaling group spanning multiple Availability Zones
Correct. ALB + multi-AZ Auto Scaling removes the single point of failure.
C.Take nightly AMI backups of the instance
Backups help recovery after data loss but do not keep the app serving during the failure.
D.Attach a second Elastic IP to the instance
Elastic IPs do not add capacity or failover across AZs.
Why this answer
An Application Load Balancer distributes traffic to healthy instances across multiple AZs, and the Auto Scaling group replaces failed instances and maintains capacity. A single instance — however large or well-backed-up — remains a single point of failure.
Correct answer: B · Last reviewed 2026-10-25
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