Q83 — AWS SOA-C02 Ch.1

Question 83 of 100 | ← Chapter 1

A SysOps administrator is managing a web application that runs on Amazon EC2 instances behind an 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?

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

Correct Answer: A. AWS/ApplicationELB HealthyHostCount <= 0

Explanation

AWS的Application Load Balancer（ALB）提供了HealthyHostCount指标，用于监控目标组中健康实例的数量。当所有实例被标记为不健康时，HealthyHostCount的值会降至0。AWS文档指出，HealthyHostCount适用于检测目标组中可用实例的整体健康状态。选项A的条件HealthyHostCount ≤ 0直接对应所有实例不健康的情况。选项B的UnhealthyHostCount ≥1仅表示至少有一个实例不健康，而非全部。选项C和D基于EC2实例状态检查，与ALB的健康检查机制无关。ALB的健康检查基于应用层配置（如HTTP响应），而EC2状态检查聚焦于实例底层基础设施状态。