- A
The destination S3 bucket does not have the correct bucket policy to allow the Lambda function to write thumbnails.
Why wrong: This would cause the Lambda function to fail during execution, not prevent invocation.
- B
The S3 event notification is configured as an asynchronous invocation, and the event is lost.
Why wrong: Option B is incorrect because S3 event notifications are asynchronous by design, but they are reliably delivered and retried if needed. Events are not typically lost due to asynchronous invocation.
- C
The Lambda function's execution role does not have permission to read from the S3 bucket.
Why wrong: The execution role is used for the Lambda function to access resources, not for S3 to invoke Lambda.
- D
The S3 bucket and the Lambda function are in different AWS regions.
S3 event notifications can only trigger Lambda functions in the same region.
Lambda Not Triggered by S3
This DVA-C02 practice question tests your understanding of development with aws services. 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 developer is building an application that processes user-uploaded images. The application uses Amazon S3 to store the images and AWS Lambda to generate thumbnails. When a user uploads an image to an S3 bucket, an S3 event notification triggers a Lambda function. The Lambda function processes the image and saves the thumbnail to another S3 bucket. The developer notices that sometimes the Lambda function is not triggered after an upload. The developer checks the Lambda function's CloudWatch logs and sees no invocation records for those uploads. The S3 bucket event notification configuration appears correct. What is the most likely cause of this issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 S3 bucket and the Lambda function are in different AWS regions.
The most likely cause is that the S3 bucket and the Lambda function are in different AWS regions (Option D). S3 event notifications for Lambda are only supported when both the bucket and the function are in the same region. If they are in different regions, the event notification will not trigger the Lambda function, and no invocation records appear in CloudWatch logs. Option A is incorrect because the destination bucket's policy affects thumbnail writes, not the trigger. Option B is incorrect because S3 event notifications are asynchronous invocations, but they are reliably delivered and not typically lost. Option C is incorrect because the Lambda function's execution role permissions affect reading from the source bucket, not the triggering mechanism.
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 destination S3 bucket does not have the correct bucket policy to allow the Lambda function to write thumbnails.
Why it's wrong here
This would cause the Lambda function to fail during execution, not prevent invocation.
- ✗
The S3 event notification is configured as an asynchronous invocation, and the event is lost.
Why it's wrong here
Option B is incorrect because S3 event notifications are asynchronous by design, but they are reliably delivered and retried if needed. Events are not typically lost due to asynchronous invocation.
- ✗
The Lambda function's execution role does not have permission to read from the S3 bucket.
Why it's wrong here
The execution role is used for the Lambda function to access resources, not for S3 to invoke Lambda.
- ✓
The S3 bucket and the Lambda function are in different AWS regions.
Why this is correct
S3 event notifications can only trigger Lambda functions in the same region.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 S3 bucket and the Lambda function are in different AWS regions. — The most likely cause is that the S3 bucket and the Lambda function are in different AWS regions (Option D). S3 event notifications for Lambda are only supported when both the bucket and the function are in the same region. If they are in different regions, the event notification will not trigger the Lambda function, and no invocation records appear in CloudWatch logs. Option A is incorrect because the destination bucket's policy affects thumbnail writes, not the trigger. Option B is incorrect because S3 event notifications are asynchronous invocations, but they are reliably delivered and not typically lost. Option C is incorrect because the Lambda function's execution role permissions affect reading from the source bucket, not the triggering mechanism.
What should I do if I get this DVA-C02 question wrong?
Identify which DVA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 20, 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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