The answer is that the target instances are unhealthy, causing the ALB to return 503 errors. This is confirmed by the access log entry showing `elb_status_code` 503 paired with `target_status_code` '-', which means the load balancer itself generated the error because it could not route the request to any healthy target—the dash indicates the request never reached an instance. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your ability to interpret ALB access logs and distinguish between errors generated by the load balancer versus those from the target. A common trap is assuming the dash means the target responded with an error, but it actually signals a failed connection due to health check failures. To remember: a dash in the target status code means the target was never in the game—think “dash = dead target.”
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 SysOps administrator is troubleshooting an application that runs on EC2 instances behind an ALB. Users report intermittent 503 errors. The administrator checks the ALB access logs and finds entries with 'elb_status_code' 503 and 'target_status_code' '-'. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The target instances are unhealthy, causing the ALB to return 503.
The ALB access log entry with `elb_status_code` 503 and `target_status_code` '-' indicates that the load balancer itself generated the 503 error because it could not establish a connection to any healthy target. The dash for the target status code means the request never reached a target instance, which occurs when all targets in the target group are marked unhealthy by the health checks. This is the most common cause of intermittent 503 errors with an ALB.
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 target instances are unhealthy, causing the ALB to return 503.
Why this is correct
If all targets are unhealthy, ALB returns 503.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The SSL certificate on the ALB has expired.
Why it's wrong here
Expired SSL would cause 502 or connection errors, not 503.
✗
The target instances have high CPU utilization.
Why it's wrong here
High CPU may cause slow responses but not necessarily 503; target_status_code would be 200 or 500.
✗
The security group on the ALB is blocking traffic.
Why it's wrong here
Security groups at ALB level would block traffic before reaching targets, resulting in no access log entry.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse a 503 error with target-side issues (like high CPU or application errors), but the dash in the target_status_code is the key indicator that the ALB itself is rejecting the request due to no healthy targets, not that the request reached a target and failed.
Detailed technical explanation
How to think about this question
The ALB performs health checks against each target instance using the configured protocol (HTTP/HTTPS/TCP) and path. If a target fails consecutive health checks (default: 5), it is marked unhealthy and removed from the routing pool. When all targets are unhealthy, the ALB returns a 503 Service Unavailable because it has no healthy endpoints to forward the request to. The `target_status_code` is '-' because the request never reached a target; the ALB short-circuits the request at the load balancer layer.
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 target instances are unhealthy, causing the ALB to return 503. — The ALB access log entry with `elb_status_code` 503 and `target_status_code` '-' indicates that the load balancer itself generated the 503 error because it could not establish a connection to any healthy target. The dash for the target status code means the request never reached a target instance, which occurs when all targets in the target group are marked unhealthy by the health checks. This is the most common cause of intermittent 503 errors with an ALB.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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