ANS-C01 Network Design Practice Question
A company has an Application Load Balancer (ALB) in front of an Auto Scaling group of EC2 instances. The ALB is configured with a target group that has a health check path of /health. Some instances are failing health checks and being marked unhealthy, but the application logs show the instances are healthy. What is the most likely cause?
⚠ Common exam trap
A common mix-up: candidates assume health check failures always indicate application problems, but The ANS-C01 exam often tests the security group misconfiguration where the ALB's health check traffic is blocked, causing a false unhealthy status despite the application being healthy.
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
✓
The security group for the instances does not allow inbound traffic from the ALB's security group on the health check port
The most likely cause is that the security group for the EC2 instances does not allow inbound traffic from the ALB's security group on the health check port. ALB health checks originate from the ALB's private IP addresses, and if the instance security group lacks an inbound rule permitting traffic from the ALB's security group (or its CIDR) on the health check port, the health check requests are dropped, causing the target to be marked unhealthy even though the application itself is running fine.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The health check path is incorrect
Why it's wrong here
The path is correctly configured as /health.
- ✗
The target group's slow start duration is too long
Why it's wrong here
Slow start does not cause health check failures.
- ✓
The security group for the instances does not allow inbound traffic from the ALB's security group on the health check port
Why this is correct
The ALB's health checks must be allowed by the instance security group.
- ✗
The ALB's stickiness is preventing health checks
Why it's wrong here
Stickiness does not affect health checks.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-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 ANS-C01 exam.