Jeff’s Note #
Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.
For AWS DVA-C02 candidates, the confusion often lies in distinguishing between the appropriate observability and debugging tools for serverless applications. In production, this is about knowing exactly how to locate slow Lambda executions without impacting performance or missing critical details. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
CloudInnovate is an online content delivery company that runs a serverless application on AWS. The frontend is a static website hosted on Amazon S3. Backend requests are handled via Amazon API Gateway which invokes multiple AWS Lambda functions. During recent traffic surges, users reported intermittent slow responses, but no errors were logged. The lead developer needs to identify which Lambda functions have slow execution periods across the fleet to improve performance and debugging.
The Requirement: #
Find a solution that allows efficient detection and analysis of slow-running Lambda executions across all functions, minimizing overhead and enabling targeted troubleshooting.
The Options #
- A) Perform a query across all the Lambda function CloudWatch Logs groups using Amazon CloudWatch Logs Insights. Filter on type “REPORT” and sort by descending Lambda function duration.
- B) Enable AWS CloudTrail Insights for the account running the Lambda functions, then review the CloudTrail Insights logs for anomalous Lambda executions.
- C) Enable AWS X-Ray tracing on all Lambda functions. Create an X-Ray group including these functions and configure an X-Ray Insight to detect performance anomalies. Review the insights once processing completes.
- D) Use AWS Glue to crawl CloudWatch Logs for Lambda functions, then run ETL jobs to structure logs and output them to S3. Finally, use a CloudWatch Dashboard to visualize the slowest functions by duration.
Google adsense #
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Correct Answer #
A
Quick Insight: The Developer Observability Imperative #
- For DVA candidates, the key is understanding the built-in capabilities of CloudWatch Logs Insights to perform fast, ad hoc querying across multiple log groups without additional overhead.
- While X-Ray offers rich tracing, it requires active tracing and can add complexity. CloudTrail Insights is not designed for Lambda execution durations. AWS Glue is over-engineered for this purpose.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Option A
The Winning Logic #
CloudWatch Logs automatically stores Lambda execution reports under each function’s log group. These report lines include the exact execution duration metadata. CloudWatch Logs Insights lets you quickly run SQL-like queries spanning multiple log groups, filtering only the “REPORT” lines, and sorting by duration descending. This provides an efficient, scalable method to drill down on slow invocations across all functions.
Additional reasons:
- No need to enable additional services (X-Ray) which may add latency or cost.
- CloudTrail Insights focuses on API call anomalies, not Lambda runtime durations.
- AWS Glue ETL + CloudWatch Dashboard is unnecessarily complex and higher latency for troubleshooting.
The Trap (Distractor Analysis): #
- Why not B? CloudTrail Insights detect anomalous API calls, not function execution times—thus unsuitable for performance profiling.
- Why not C? AWS X-Ray provides deep tracing but requires active tracing and sampling setup. For simple duration queries across many functions, this is overkill and slower to get results.
- Why not D? Glue ETL jobs add complexity and delay. Logs are best queried directly in CloudWatch for performance investigations rather than heavy ETL processing.
The Technical Blueprint #
Developer CLI Example: Querying Lambda execution duration with CloudWatch Logs Insights #
aws logs start-query \
--log-group-names '/aws/lambda/my-function-1' '/aws/lambda/my-function-2' \
--start-time $(($(date +%s) - 3600)) \
--end-time $(date +%s) \
--query-string 'fields @timestamp, @message | filter @message like /REPORT/ | parse @message /Duration: (?<duration>\\d+.\\d+) ms/ | sort duration desc | limit 20'
This command queries the last hour of logs across two Lambda function log groups, filters on REPORT lines, extracts execution duration, and lists the slowest executions.
The Comparative Analysis #
| Option | API/Service Complexity | Performance | Practical Use Case |
|---|---|---|---|
| A | Low | High | Fast querying of Lambda logs for duration, immediate troubleshooting |
| B | Medium | Low | Detects account-level API anomalies, not function duration |
| C | High | Medium | Deep tracing, useful for root cause analysis post identification |
| D | Very High | Low | Complex log processing—overkill for latency analysis |
Real-World Application (Practitioner Insight) #
Exam Rule #
For the exam, always pick CloudWatch Logs Insights when you need to query Lambda execution durations across multiple functions.
Real World #
In a production environment, X-Ray tracing would complement Logs Insights for deep dive issues, but Logs Insights is your first line of investigation for quick latency profiling.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS DVA-C02 exam.