The answer is to use CloudWatch metrics published by Lambda and create a CloudWatch alarm on the ErrorCount metric with a math expression to calculate error rate. Lambda automatically emits key metrics—Invocations, Duration, and ErrorCount—to CloudWatch with no additional setup, making this the minimal-effort solution. By creating a CloudWatch alarm that uses a math expression (such as `ERRORS / INVOCATIONS * 100`), you can trigger an alarm when the error rate exceeds 5% over a 5-minute period. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of native metric integration versus over-engineering with tools like CloudTrail or Lambda Insights. A common trap is choosing CloudTrail for monitoring errors, but CloudTrail records API calls, not function execution metrics. Another pitfall is reaching for CloudWatch Logs Insights, which requires parsing logs when the metrics are already available. Memory tip: remember that Lambda’s built-in CloudWatch metrics are the “zero-config” foundation for error rate alarms—think “Lambda emits, CloudWatch alarms.”
DOP-C02 Monitoring and Logging Practice Question
This DOP-C02 practice question tests your understanding of monitoring and logging. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 AWS Lambda functions for data processing. The operations team needs to monitor the number of invocations, duration, and error counts for each function. They also want to set alarms when the error rate exceeds 5% in a 5-minute period. Which combination of AWS services should the team use to achieve this with minimal effort?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use CloudWatch metrics published by Lambda and create a CloudWatch alarm on the ErrorCount metric with a math expression to calculate error rate.
Option B is correct because Lambda automatically publishes metrics to CloudWatch (invocations, duration, errors, etc.). CloudWatch Alarms can be set on the ErrorCount metric, and a math expression can calculate error rate. Option A is wrong because CloudTrail logs API calls, not function execution metrics. Option C is wrong because CloudWatch Logs Insights is for log analysis, but the metrics are already available. Option D is wrong because Lambda Insights is for detailed performance monitoring but is not necessary for basic metrics and alarms.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 AWS CloudTrail to log Lambda invocations and configure CloudWatch alarms on the log events.
Why it's wrong here
CloudTrail logs API calls, not function execution metrics.
✗
Enable Lambda Insights to collect detailed metrics and use CloudWatch dashboards to monitor error rates.
Why it's wrong here
Lambda Insights is overkill for simple metric monitoring.
✗
Stream Lambda logs to CloudWatch Logs and use CloudWatch Logs Insights to query error rates, then create alarms.
Why it's wrong here
Metrics are already available; no need to query logs.
✓
Use CloudWatch metrics published by Lambda and create a CloudWatch alarm on the ErrorCount metric with a math expression to calculate error rate.
Why this is correct
Lambda emits metrics automatically; alarms can be set directly.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. 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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
Monitoring and Logging — This question tests Monitoring and Logging — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use CloudWatch metrics published by Lambda and create a CloudWatch alarm on the ErrorCount metric with a math expression to calculate error rate. — Option B is correct because Lambda automatically publishes metrics to CloudWatch (invocations, duration, errors, etc.). CloudWatch Alarms can be set on the ErrorCount metric, and a math expression can calculate error rate. Option A is wrong because CloudTrail logs API calls, not function execution metrics. Option C is wrong because CloudWatch Logs Insights is for log analysis, but the metrics are already available. Option D is wrong because Lambda Insights is for detailed performance monitoring but is not necessary for basic metrics and alarms.
What should I do if I get this DOP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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