Question

A company runs a stateless web application on EC2 instances behind an Application Load Balancer (ALB) spread across three Availability Zones. An Auto Scaling group maintains 3 instances per AZ. During a recent single-AZ impairment, monitoring showed that clients connected through the affected AZ received elevated latency and some 5xx errors even though healthy instances existed in the other two AZs. The DevOps team wants to ensure that a single-AZ failure does not degrade the user experience, with minimal ongoing management. Which action BEST addresses this requirement?

Accepted Answer

Confirm cross-zone load balancing is enabled on the ALB so requests are distributed evenly to healthy targets in all AZs regardless of which AZ received the request.

Answer

Enable ALB health checks with a lower unhealthy threshold and rely on the Auto Scaling group to replace failed instances in the impaired AZ.

Answer

Configure Route 53 latency-based routing with health checks pointing to per-AZ ALB nodes so traffic avoids the impaired AZ.

Answer

Increase the Auto Scaling group desired capacity and use a target tracking policy on ALB request count to add capacity when an AZ fails.