- A
View the Amazon CloudWatch Logs log group for the Lambda function to see the function's output and error messages.
Custom resource Lambda functions log to CloudWatch Logs; reviewing those logs helps identify the failure.
- B
Update the Lambda function code to include additional logging and then re-execute the stack update.
Why wrong: This is a possible solution but not the first step; you need to see existing logs first.
- C
Check the Amazon S3 bucket where the Lambda function code is stored for any access denied errors.
Why wrong: S3 bucket policy issues would cause function to not even start.
- D
Review the CloudFormation stack events in the AWS Management Console for detailed error messages from the Lambda function.
Why wrong: Stack events show status but not detailed logs from the Lambda function.
Quick Answer
The answer is to view the Amazon CloudWatch Logs log group for the Lambda function, as this is the most direct and reliable method to debug a CloudFormation custom resource Lambda failure. This works because every Lambda function invoked by a custom resource automatically streams its stdout, stderr, and any print or console.log statements to a log group named /aws/lambda/<function-name>, which captures the exact error messages or return values that caused the stack to roll back. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding of the CloudFormation custom resource lifecycle and the fact that Lambda logs are the primary debugging tool—no stack modification or new update is needed. A common trap is trying to re-run the stack update or check the template syntax first, but the logs always hold the immediate failure details. Memory tip: think “Lambda logs first, never guess the error.”
DOP-C02 Configuration Management and IaC Practice Question
This DOP-C02 practice question tests your understanding of configuration management and iac. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 uses AWS CloudFormation to manage its infrastructure. The CloudFormation template includes a custom resource backed by an AWS Lambda function that validates a condition and returns a value. During a stack update, the custom resource fails, and the stack rolls back. The DevOps engineer needs to debug the issue. Which steps should be taken to troubleshoot the custom resource failure?
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
View the Amazon CloudWatch Logs log group for the Lambda function to see the function's output and error messages.
Option A is correct because AWS Lambda functions invoked by CloudFormation custom resources automatically send their logs to Amazon CloudWatch Logs. By examining the log group named `/aws/lambda/<function-name>`, the DevOps engineer can view the function's `stdout`, `stderr`, and any `print()` or `console.log()` statements, which will contain the exact error messages or return values that caused the custom resource to fail. This is the most direct and reliable method to debug the failure without modifying the stack or waiting for a new update.
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.
- ✓
View the Amazon CloudWatch Logs log group for the Lambda function to see the function's output and error messages.
Why this is correct
Custom resource Lambda functions log to CloudWatch Logs; reviewing those logs helps identify the failure.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Update the Lambda function code to include additional logging and then re-execute the stack update.
Why it's wrong here
This is a possible solution but not the first step; you need to see existing logs first.
- ✗
Check the Amazon S3 bucket where the Lambda function code is stored for any access denied errors.
Why it's wrong here
S3 bucket policy issues would cause function to not even start.
- ✗
Review the CloudFormation stack events in the AWS Management Console for detailed error messages from the Lambda function.
Why it's wrong here
Stack events show status but not detailed logs from the Lambda function.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume CloudFormation stack events provide detailed error messages from the Lambda function, but in reality, they only show generic failure statuses, while the actual debugging data resides in CloudWatch Logs.
Trap categories for this question
Command / output trap
Stack events show status but not detailed logs from the Lambda function.
Detailed technical explanation
How to think about this question
When a custom resource is invoked, CloudFormation expects the Lambda function to send a response to a pre-signed Amazon S3 URL using the `cfn-response` module or a custom HTTP request. If the function fails to send a response (e.g., due to an unhandled exception, timeout, or missing `Status` field), CloudFormation treats it as a failure and triggers a rollback. The CloudWatch Logs log group captures the exact exception stack trace or the response payload, which is essential for debugging. Additionally, the function must include the `functionName` in the response to correlate logs, and the log group is created automatically when the function is first invoked.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Configuration Management and IaC — This question tests Configuration Management and IaC — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: View the Amazon CloudWatch Logs log group for the Lambda function to see the function's output and error messages. — Option A is correct because AWS Lambda functions invoked by CloudFormation custom resources automatically send their logs to Amazon CloudWatch Logs. By examining the log group named `/aws/lambda/<function-name>`, the DevOps engineer can view the function's `stdout`, `stderr`, and any `print()` or `console.log()` statements, which will contain the exact error messages or return values that caused the custom resource to fail. This is the most direct and reliable method to debug the failure without modifying the stack or waiting for a new update.
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 24, 2026
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