- A
Create a CloudWatch Logs metric filter that counts log events containing 'DuplicateTransaction' and set an alarm on the metric with a threshold of 10.
Metric filters are designed for real-time pattern matching on logs and can generate custom metrics.
- B
Use DynamoDB Streams to trigger a Lambda function that counts duplicates and publishes metrics.
Why wrong: DynamoDB Streams would capture data changes, not log events; also adds significant complexity.
- C
Stream the CloudWatch Logs to Amazon Kinesis Data Analytics and use SQL queries to detect duplicates.
Why wrong: Overly complex and costly for a simple count-based alert.
- D
Modify the Lambda function to publish a custom metric to CloudWatch for each duplicate transaction, then set an alarm.
Why wrong: This requires code changes and adds latency; also, the question asks for efficient monitoring without modifying the application.
Quick Answer
The answer is to create a CloudWatch Logs metric filter that counts log events containing 'DuplicateTransaction' and set an alarm on the metric with a threshold of 10. This is the most efficient approach because a metric filter continuously scans incoming log events for a specified pattern—in this case, the duplicate transaction identifier—and increments a custom CloudWatch metric each time the pattern is matched, allowing you to alarm directly on that metric without any additional infrastructure. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of CloudWatch Logs as a real-time monitoring source and the common trap of overcomplicating solutions with services like Kinesis or DynamoDB Streams when a simple metric filter suffices. Remember the memory tip: "Filter logs, count patterns, alarm on metrics"—if you can count a string in a log, you don’t need a stream.
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 runs a serverless application using AWS Lambda, Amazon API Gateway, and Amazon DynamoDB. The application processes financial transactions. The DevOps team needs to monitor for duplicate transactions that could occur due to retries. The team wants to set up an alert when the number of duplicate transaction attempts exceeds 10 in a 5-minute window. The application logs each transaction attempt with a unique transaction ID to CloudWatch Logs. What is the most efficient way to achieve this?
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
Create a CloudWatch Logs metric filter that counts log events containing 'DuplicateTransaction' and set an alarm on the metric with a threshold of 10.
Option A is correct because a metric filter on CloudWatch Logs can count occurrences of a pattern (e.g., duplicate transaction ID) and create a custom metric, which can then trigger an alarm. Option B is wrong because Lambda sends logs to CloudWatch Logs, not directly to CloudWatch Metrics. Option C is wrong because Kinesis Data Analytics would add unnecessary complexity and cost. Option D is wrong because DynamoDB Streams and Lambda add latency and complexity for a simple counting task.
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.
- ✓
Create a CloudWatch Logs metric filter that counts log events containing 'DuplicateTransaction' and set an alarm on the metric with a threshold of 10.
- ✗
Use DynamoDB Streams to trigger a Lambda function that counts duplicates and publishes metrics.
Why it's wrong here
DynamoDB Streams would capture data changes, not log events; also adds significant complexity.
- ✗
Stream the CloudWatch Logs to Amazon Kinesis Data Analytics and use SQL queries to detect duplicates.
Why it's wrong here
Overly complex and costly for a simple count-based alert.
- ✗
Modify the Lambda function to publish a custom metric to CloudWatch for each duplicate transaction, then set an alarm.
Why it's wrong here
This requires code changes and adds latency; also, the question asks for efficient monitoring without modifying the application.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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.
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Monitoring and Logging — study guide chapter
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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 — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Create a CloudWatch Logs metric filter that counts log events containing 'DuplicateTransaction' and set an alarm on the metric with a threshold of 10. — Option A is correct because a metric filter on CloudWatch Logs can count occurrences of a pattern (e.g., duplicate transaction ID) and create a custom metric, which can then trigger an alarm. Option B is wrong because Lambda sends logs to CloudWatch Logs, not directly to CloudWatch Metrics. Option C is wrong because Kinesis Data Analytics would add unnecessary complexity and cost. Option D is wrong because DynamoDB Streams and Lambda add latency and complexity for a simple counting task.
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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Last reviewed: Jun 20, 2026
This DOP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DOP-C02 exam.
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