- A
The Lambda function must send a response to an S3 pre-signed URL.
Custom resources require the function to respond to the pre-signed URL.
- B
The Lambda function must be defined in the same CloudFormation template.
Why wrong: The function can be defined elsewhere.
- C
The Lambda function must return a JSON object with the desired output.
Why wrong: The function must send a response to a pre-signed URL.
- D
The Lambda function must be written in Python.
Why wrong: Any supported runtime can be used.
Question 55 of 1,616
Why CloudFormation Custom Resource Lambda Fails Without Response
This DVA-C02 practice question tests your understanding of development with aws services. 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 CloudFormation to deploy infrastructure. The developer wants to create a custom resource that runs a Lambda function during stack creation and update. What must the developer do to ensure the custom resource works correctly?
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
✓
The Lambda function must send a response to an S3 pre-signed URL.
Option A is correct because AWS CloudFormation custom resources require the Lambda function to send a response to an S3 pre-signed URL to signal completion. CloudFormation waits for this response to proceed with stack operations; without it, the stack creation or update will time out and fail.
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.
- ✓
The Lambda function must send a response to an S3 pre-signed URL.
Why this is correct
Custom resources require the function to respond to the pre-signed URL.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The Lambda function must be defined in the same CloudFormation template.
Why it's wrong here
The function can be defined elsewhere.
- ✗
The Lambda function must return a JSON object with the desired output.
Why it's wrong here
The function must send a response to a pre-signed URL.
- ✗
The Lambda function must be written in Python.
Why it's wrong here
Any supported runtime can be used.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the Lambda function's return value is automatically captured by CloudFormation, but in reality, the function must explicitly send a response to the pre-signed URL to signal completion.
Detailed technical explanation
How to think about this question
Under the hood, CloudFormation generates a pre-signed S3 URL and passes it to the custom resource via the `ResponseURL` property in the event payload. The Lambda function must send a PUT request to this URL with a JSON body containing `Status` (SUCCESS or FAILED), `PhysicalResourceId`, and optional `Data`. If the function fails to respond within one hour, CloudFormation marks the stack operation as failed. This mechanism is critical for integrating external provisioning actions that are not natively supported by CloudFormation resources.
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.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Development with AWS Services — This question tests Development with AWS Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Lambda function must send a response to an S3 pre-signed URL. — Option A is correct because AWS CloudFormation custom resources require the Lambda function to send a response to an S3 pre-signed URL to signal completion. CloudFormation waits for this response to proceed with stack operations; without it, the stack creation or update will time out and fail.
What should I do if I get this DVA-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: Jul 4, 2026
This DVA-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 DVA-C02 exam.
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