AWS Certified SysOps Administrator – Associate (legacy) — Question 501

A SysOps Administrator is managing a web application that runs on Amazon EC2 instances behind an ELB Application Load Balancer (ALB). The instances run in an EC2 Auto Scaling group. The administrator wants to set an alarm for when all target instances associated with the ALB are unhealthy.
Which condition should be used with the alarm?

Answer options

• A. AWS/ApplicationELB HealthyHostCount <= 0
• B. AWS/ApplicationELB UnhealthyHostCount >= 1
• C. AWS/EC2 StatusCheckFailed <= 0
• D. AWS/EC2 StatusCheckFailed >= 1

Correct answer: A

Explanation

To detect when all targets behind the ALB are unhealthy, the AWS/ApplicationELB HealthyHostCount metric must be monitored, and an alarm should trigger when it falls to 0 or less. The UnhealthyHostCount metric only indicates if any single host is unhealthy, which does not guarantee that all hosts are down. EC2 StatusCheckFailed metrics monitor individual instance platform and system health rather than the ALB target group health status.