The correct answer is to use the ALB HealthyHostCount metric with a statistic of Sum and a threshold set to 0.5 multiplied by the Auto Scaling group’s desired capacity. This works because HealthyHostCount directly reports the number of registered instances passing health checks, and using Sum aggregates the total count over the evaluation period, allowing you to compare it against half the desired capacity. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding that ALB metrics like HealthyHostCount are per-target-group, and the common trap is choosing Average instead of Sum, which would incorrectly normalize the count. For the alarm to trigger when healthy hosts drop below 50% for more than 5 minutes, you configure the threshold as 0.5 * desired capacity with a Sum statistic over a 5-minute period. Memory tip: “Sum the healthy count, then halve the desired—if the sum falls below that line, the alarm is fired.”
SOA-C02 Monitoring, Logging, and Remediation Practice Question
This SOA-C02 practice question tests your understanding of monitoring, logging, and remediation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 is using Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. The operations team needs to receive an alert when the number of healthy hosts drops below 50% of the desired capacity for more than 5 minutes. Which CloudWatch metric and alarm configuration should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the 'HealthyHostCount' metric with a statistic of 'Sum' and a threshold of 0.5 * desired capacity.
The correct answer is B because the 'HealthyHostCount' metric from the Application Load Balancer (ALB) directly reports the number of registered instances that are passing health checks. By setting the statistic to 'Sum' and the threshold to 0.5 * desired capacity, the alarm triggers when the count of healthy hosts falls below 50% of the Auto Scaling group's desired capacity for the specified evaluation period of 5 minutes, meeting the exact requirement.
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.
✗
Use the 'RequestCount' metric with a statistic of 'Sum' and a threshold of 50% of the average request count.
Why it's wrong here
'RequestCount' does not reflect host health; it measures traffic volume.
✓
Use the 'HealthyHostCount' metric with a statistic of 'Sum' and a threshold of 0.5 * desired capacity.
Why this is correct
This directly measures the number of healthy hosts and can be compared to half the desired capacity.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use the 'UnhealthyHostCount' metric with a threshold of 50% of desired capacity.
Why it's wrong here
'UnhealthyHostCount' measures unhealthy instances, not healthy, and would require a different threshold logic.
✗
Use the 'TargetResponseTime' metric with a statistic of 'p90' and a threshold of 2 seconds.
Why it's wrong here
This measures latency, not host health.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'UnhealthyHostCount' with 'HealthyHostCount', assuming that a threshold on unhealthy hosts (e.g., >50% of desired capacity) is equivalent, but this fails because the alarm would not trigger correctly when the total number of hosts changes or when both healthy and unhealthy counts shift simultaneously.
Detailed technical explanation
How to think about this question
The 'HealthyHostCount' metric is emitted by the ALB every 60 seconds and represents the number of targets that are considered healthy based on the configured health check settings (e.g., HTTP 200 responses). The 'Sum' statistic aggregates the count over the evaluation period, and the threshold must be calculated as a static value (e.g., 0.5 * desired capacity) because CloudWatch does not support dynamic thresholds based on Auto Scaling group capacity; the desired capacity must be known and set manually or via a custom metric. In a real-world scenario, if the Auto Scaling group scales out, the threshold would need to be updated to maintain the 50% condition, which is a common operational challenge.
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: Use the 'HealthyHostCount' metric with a statistic of 'Sum' and a threshold of 0.5 * desired capacity. — The correct answer is B because the 'HealthyHostCount' metric from the Application Load Balancer (ALB) directly reports the number of registered instances that are passing health checks. By setting the statistic to 'Sum' and the threshold to 0.5 * desired capacity, the alarm triggers when the count of healthy hosts falls below 50% of the Auto Scaling group's desired capacity for the specified evaluation period of 5 minutes, meeting the exact requirement.
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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