The answer is a full ALB surge queue, and the metric to check is SurgeQueueLength. This is correct because when an Application Load Balancer receives more traffic than it can process, it buffers excess requests in a surge queue; once that queue reaches its capacity, the ALB immediately rejects new requests with a 503 error, even if the target instances themselves are healthy. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding that a 503 does not always mean the targets are failing—it can indicate the load balancer itself is overwhelmed. A common trap is to focus on target health metrics like UnhealthyHostCount, but the key insight is that the ALB’s internal capacity is the bottleneck. Remember: if targets are green but you see 503s, think “surge queue full”—the mnemonic “503 = Surge Queue Full” can save you on exam day.
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 uses an Application Load Balancer (ALB) to distribute traffic to a fleet of EC2 instances. The administrator notices that the ALB returns 503 errors during peak traffic. The instances are healthy according to the ALB health checks. What is the MOST likely cause and what metric should the administrator check?
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 ALB's surge queue is full; check the SurgeQueueLength metric.
The ALB returns 503 errors despite healthy targets, which indicates that the ALB itself is overwhelmed and cannot process incoming requests. The ALB uses a surge queue to buffer requests when traffic exceeds its capacity; when the queue is full, new requests are rejected with a 503. The SurgeQueueLength metric directly measures this queue depth, making it the correct metric to check.
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 SSL certificate has expired; check the TLS handshake errors.
Why it's wrong here
SSL errors would cause different HTTP error codes, not 503.
✗
The ALB is overloaded; check the ALB's CPUUtilization metric.
The targets are failing health checks; check the HealthyHostCount metric.
Why it's wrong here
HealthyHostCount would be low if targets are unhealthy, but the scenario says instances are healthy.
✓
The ALB's surge queue is full; check the SurgeQueueLength metric.
Why this is correct
The SurgeQueueLength metric indicates the number of pending requests waiting to be routed. A high value can cause 503 errors.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse ALB overload (surge queue full) with target health issues, but the question explicitly states healthy targets, so the root cause is the ALB's own capacity limit, not the targets.
Trap categories for this question
Scenario analysis trap
HealthyHostCount would be low if targets are unhealthy, but the scenario says instances are healthy.
Detailed technical explanation
How to think about this question
The ALB surge queue is a per-node buffer that holds incoming requests when the number of concurrent connections exceeds the target group's capacity. The default surge queue size is 1024 per ALB node; when this fills, the ALB returns 503. The SurgeQueueLength metric should be monitored with a threshold of 0 or near 0; sustained values above 0 indicate the ALB is bottlenecked and needs more targets or a higher connection limit.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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 ALB's surge queue is full; check the SurgeQueueLength metric. — The ALB returns 503 errors despite healthy targets, which indicates that the ALB itself is overwhelmed and cannot process incoming requests. The ALB uses a surge queue to buffer requests when traffic exceeds its capacity; when the queue is full, new requests are rejected with a 503. The SurgeQueueLength metric directly measures this queue depth, making it the correct metric to check.
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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