DVA-C02 Development with AWS Services Practice Question
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 a serverless application that processes images uploaded to an S3 bucket. The bucket triggers a Lambda function that creates a thumbnail and stores it in another S3 bucket. The developer notices that the Lambda function is invoked multiple times for the same object, causing duplicate thumbnails. What is the MOST likely cause?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The S3 bucket has multiple event notifications that trigger the same Lambda function.
Option D is correct because if S3 event notifications are misconfigured (e.g., both PutObject and PutObjectAcl events trigger the same function), the function runs multiple times. Option A is wrong because Lambda provides at-least-once execution, but duplicates are not typical unless triggered multiple times. Option B is wrong because S3 does not send duplicate events; the issue is multiple triggers. Option C is wrong because concurrent Lambda executions would not cause duplicates; each invocation processes a unique event.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
S3 event notifications are eventually consistent and may deliver duplicates.
Why it's wrong here
S3 notifications are generally reliable; duplicates are not a known consistency issue.
✗
The Lambda function is configured with a DLQ that causes retries.
Why it's wrong here
A DLQ is for failed messages; successful invocations do not retry.
✗
The Lambda function is idempotent and should handle duplicates.
Why it's wrong here
While idempotency is good practice, the question asks the cause, not the solution.
✓
The S3 bucket has multiple event notifications that trigger the same Lambda function.
Why this is correct
Multiple notifications (e.g., for different event types) can cause the same function to be invoked for the same object.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DVA-C02 ACL questions on filtering logic and placement.
Development with AWS Services — This question tests Development with AWS Services — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The S3 bucket has multiple event notifications that trigger the same Lambda function. — Option D is correct because if S3 event notifications are misconfigured (e.g., both PutObject and PutObjectAcl events trigger the same function), the function runs multiple times. Option A is wrong because Lambda provides at-least-once execution, but duplicates are not typical unless triggered multiple times. Option B is wrong because S3 does not send duplicate events; the issue is multiple triggers. Option C is wrong because concurrent Lambda executions would not cause duplicates; each invocation processes a unique event.
What should I do if I get this DVA-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DVA-C02 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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