PAS-C01 Operations and Maintenance Practice Question
A company runs a production web application on EC2 instances behind an ALB. The operations team receives an alert that the application is returning HTTP 503 errors. Which THREE steps should be taken to diagnose the issue?
⚠ Common exam trap
The PAS-C01 exam often tests the misconception that CPU utilization or instance-level metrics are the primary cause of 503 errors, when in reality the ALB's health check mechanism and target group configuration are the direct cause, and CPU issues are only one possible underlying reason for health check failures.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check the ALB's HealthyHostCount metric in CloudWatch.
The ALB's HealthyHostCount metric in CloudWatch shows the number of healthy targets registered to the target group. A value of zero or a persistent drop indicates that all EC2 instances are failing health checks, which directly causes HTTP 503 errors because the ALB has no healthy targets to forward traffic to. This metric is the first place to check when diagnosing 503 errors, as it pinpoints whether the issue is with target health rather than network connectivity or load.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Review VPC Flow Logs to identify if traffic is reaching the ALB.
Why it's wrong here
Flow logs show network-level traffic, not application-level errors.
- ✓
Check the ALB's HealthyHostCount metric in CloudWatch.
Why this is correct
Indicates if targets are passing health checks.
- ✓
Check the CPU utilization of the EC2 instances in the Auto Scaling group.
Why this is correct
High CPU can cause instances to fail health checks.
- ✓
Verify the health check settings on the target group.
Why this is correct
Misconfigured health checks can cause all targets to be considered unhealthy.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PAS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PAS-C01 exam.