The answer is a health check path returning HTTP 503. This is correct because the Application Load Balancer (ALB) marks an instance as unhealthy when its health check receives any non-2xx or non-3xx response, and a 503 Service Unavailable error specifically means the application is reachable but failing to serve the request—so the instance appears in service yet the healthy host count drops. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding that a 503 response is an application-layer failure, not a network or security group issue; a common trap is assuming the problem is with security groups or instance state when the real culprit is the application’s health check endpoint. To troubleshoot low healthy host count, always verify the exact HTTP status code the health check receives, not just that the instance is running. Memory tip: “503 means the app is alive but not thriving—check your code, not your cloud.”
SOA-C02 Monitoring, Logging, and Remediation Practice Question
This SOA-C02 practice question tests your understanding of monitoring, logging, and remediation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company has an Auto Scaling group of EC2 instances behind an Application Load Balancer. The SysOps administrator notices that the healthy host count is lower than expected. The instances are in service, and security groups allow traffic. What is a likely cause?
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 returning HTTP 503.
The correct answer is C because a health check path returning HTTP 503 (Service Unavailable) indicates that the target instances are reachable but the application is failing to respond correctly. The Application Load Balancer (ALB) marks instances as unhealthy when the health check receives any non-2xx or non-3xx response, which reduces the healthy host count even though the instances are in service and security groups are properly configured.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 instances are not registered with the target group.
Why it's wrong here
They are in service, so they are registered.
✗
The security group for the load balancer does not allow inbound traffic.
Why it's wrong here
Security groups are permissive.
✓
The health check path is returning HTTP 503.
Why this is correct
A non-200 response causes the instance to be unhealthy.
Related concept
Read the scenario before looking for a memorised answer.
✗
The target group is not associated with the load balancer.
Why it's wrong here
If not associated, instances would not be in service.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a low healthy host count is always due to network-level issues (security groups or registration), but the question explicitly states instances are 'in service' and security groups allow traffic, pointing to an application-level health check failure like a 503 response.
Detailed technical explanation
How to think about this question
The ALB health check system sends HTTP requests to the configured path (e.g., /health) every HealthCheckIntervalSeconds (default 30). A 503 response is treated as unhealthy because it indicates the application layer is failing, often due to resource exhaustion, database connectivity issues, or application errors. This is distinct from a connection timeout (which would indicate network or security group issues) or a 200 response (healthy). In real-world scenarios, a misconfigured health check path that returns 503 due to a missing dependency (e.g., a backend database) is a common cause of unexpected unhealthy instances.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Monitoring, Logging, and Remediation — This question tests Monitoring, Logging, and Remediation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The health check path is returning HTTP 503. — The correct answer is C because a health check path returning HTTP 503 (Service Unavailable) indicates that the target instances are reachable but the application is failing to respond correctly. The Application Load Balancer (ALB) marks instances as unhealthy when the health check receives any non-2xx or non-3xx response, which reduces the healthy host count even though the instances are in service and security groups are properly configured.
What should I do if I get this SOA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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