SAP-C02 Continuous Improvement for Existing Solutions Practice Question
A company runs a web application on EC2 instances behind an ALB. Users report intermittent 503 errors during peak hours. The metrics show the target group's healthy host count drops to zero periodically. What is the most likely cause?
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 health check path is misconfigured and returns HTTP 404.
The ALB performs health checks on targets by sending requests to the configured health check path. If the health check path returns an HTTP 404 (or any non-200 status), the ALB marks the target as unhealthy. When all instances have a misconfigured health check path that returns 404, the healthy host count drops to zero, resulting in 503 errors. Option D is correct because a misconfigured health check path directly causes all instances to be marked unhealthy. Option A (idle timeout) would cause connection timeouts but not affect healthy host count. Option B (security group) would prevent traffic from ALB, but the health check would still succeed if the security group allows ALB traffic, and it would not cause healthy host count to drop to zero periodically if misconfigured. Option C (insufficient capacity) would cause scaling issues but not zero healthy hosts if the health check is correct. Therefore, D is the most likely cause.
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 ALB's idle timeout is set too low.
Why it's wrong here
A low idle timeout would cause connection drops, not a drop in healthy host count.
- ✗
The security group for the EC2 instances does not allow inbound traffic from the ALB.
Why it's wrong here
This would cause health checks to fail with no response, but the healthy host count would drop to zero only if all instances are affected; however, the more likely first step is a health check path issue.
- ✗
The EC2 instances are in an Auto Scaling group with insufficient capacity.
Why it's wrong here
Insufficient capacity would reduce the number of instances, but the healthy host count would not drop to zero if some instances are running.
- ✓
The health check path is misconfigured and returns HTTP 404.
Why this is correct
A 404 response causes the ALB to mark the instance as unhealthy, reducing the healthy host count.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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