- A
Enable CloudWatch Logs for the ALB and use CloudWatch Logs Insights to query 5xx logs, then create a metric filter and alarm.
Why wrong: Incorrect: This is possible but not the simplest or most direct method; the ALB already provides 5xx metrics.
- B
Configure AWS Config rules to check ALB 5xx error counts and trigger alarms.
Why wrong: Incorrect: AWS Config is for configuration compliance, not real-time error monitoring.
- C
Use CloudWatch ALB metrics (HTTPCode_ELB_5XX_Count) and create a CloudWatch Alarm on the Sum statistic with a threshold based on total request count.
Correct: ALB publishes HTTP 5xx metrics to CloudWatch, and alarms can be set on these metrics.
- D
Use AWS X-Ray to trace requests and create a CloudWatch alarm based on X-Ray error rate.
Why wrong: Incorrect: X-Ray is for tracing, not for aggregate error rate monitoring.
Quick Answer
The answer is to use CloudWatch ALB metrics with a math expression, specifically combining the `HTTPCode_ELB_5XX_Count` metric (using the Sum statistic) with the `RequestCount` metric to calculate the error rate as a percentage. This is correct because an ALB 5xx error rate CloudWatch alarm cannot be based solely on raw error counts; the threshold must reflect the ratio of errors to total requests over the 5-minute period, which requires a CloudWatch metric math expression like `m1/m2*100 > 5` or a composite alarm. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this tests your understanding that ALB metrics are automatically published but that rate-based alarms demand math expressions rather than simple threshold alarms—a common trap is choosing a raw count alarm on `HTTPCode_ELB_5XX_Count` alone. Remember the memory tip: “5xx rate needs a ratio, not a raw number.”
DOP-C02 Monitoring and Logging Practice Question
This DOP-C02 practice question tests your understanding of monitoring and logging. 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 running a critical web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The DevOps team wants to monitor HTTP 5xx errors and receive alerts when the error rate exceeds 5% over a 5-minute period. Which combination of services and configurations should be used to meet these requirements?
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
Use CloudWatch ALB metrics (HTTPCode_ELB_5XX_Count) and create a CloudWatch Alarm on the Sum statistic with a threshold based on total request count.
Option C is correct because ALB automatically publishes the `HTTPCode_ELB_5XX_Count` metric to CloudWatch, and you can create a CloudWatch alarm using the `Sum` statistic over a 5-minute period. To detect when the error rate exceeds 5%, you need to combine this metric with the `RequestCount` metric in a math expression (e.g., `m1/m2*100 > 5`) or use a composite alarm, as the alarm threshold must be based on the ratio of 5xx errors to total requests, not just the raw count.
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.
- ✗
Enable CloudWatch Logs for the ALB and use CloudWatch Logs Insights to query 5xx logs, then create a metric filter and alarm.
Why it's wrong here
Incorrect: This is possible but not the simplest or most direct method; the ALB already provides 5xx metrics.
- ✗
Configure AWS Config rules to check ALB 5xx error counts and trigger alarms.
Why it's wrong here
Incorrect: AWS Config is for configuration compliance, not real-time error monitoring.
- ✓
Use CloudWatch ALB metrics (HTTPCode_ELB_5XX_Count) and create a CloudWatch Alarm on the Sum statistic with a threshold based on total request count.
Why this is correct
Correct: ALB publishes HTTP 5xx metrics to CloudWatch, and alarms can be set on these metrics.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use AWS X-Ray to trace requests and create a CloudWatch alarm based on X-Ray error rate.
Why it's wrong here
Incorrect: X-Ray is for tracing, not for aggregate error rate monitoring.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume they need to parse logs (Option A) or use a separate tracing service (Option D) for error rate monitoring, when in fact the ALB's built-in CloudWatch metrics and metric math provide a simpler, real-time, and cost-effective solution without additional log ingestion or query overhead.
Detailed technical explanation
How to think about this question
Under the hood, the ALB publishes `HTTPCode_ELB_5XX_Count` and `RequestCount` metrics every minute to CloudWatch. To calculate an error rate exceeding 5% over 5 minutes, you can use a CloudWatch metric math expression like `(m1 / m2) * 100` where `m1` is the sum of `HTTPCode_ELB_5XX_Count` and `m2` is the sum of `RequestCount` over the same period, then set an alarm on the result. A subtle behavior is that the ALB also reports `HTTPCode_Target_5XX_Count` for errors from the target instances, so you must ensure you are monitoring the correct metric (ELB-level vs. target-level) depending on whether you want to catch load balancer-generated errors or backend errors.
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
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Monitoring and Logging — This question tests Monitoring and Logging — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use CloudWatch ALB metrics (HTTPCode_ELB_5XX_Count) and create a CloudWatch Alarm on the Sum statistic with a threshold based on total request count. — Option C is correct because ALB automatically publishes the `HTTPCode_ELB_5XX_Count` metric to CloudWatch, and you can create a CloudWatch alarm using the `Sum` statistic over a 5-minute period. To detect when the error rate exceeds 5%, you need to combine this metric with the `RequestCount` metric in a math expression (e.g., `m1/m2*100 > 5`) or use a composite alarm, as the alarm threshold must be based on the ratio of 5xx errors to total requests, not just the raw count.
What should I do if I get this DOP-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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Last reviewed: Jun 11, 2026
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