- A
Store the object key and event ID in a DynamoDB table and check for duplicates before processing
By recording processed object keys in DynamoDB and checking for existing records, the function can skip duplicate events, ensuring each object is processed only once.
- B
Set the Lambda function's concurrency to 1 to prevent concurrent executions
Why wrong: Limiting concurrency does not prevent duplicate events; it only ensures that only one invocation runs at a time, but duplicate events can still arrive and be processed sequentially.
- C
Use an Amazon SQS FIFO queue as the event destination
Why wrong: S3 event notifications cannot be sent to FIFO queues; only standard queues are supported.
- D
Enable S3 event notification filtering based on object size
Why wrong: Filtering based on object size controls which objects trigger events, but does not prevent duplicates for objects that match the filter.
DVA-C02 Development with AWS Services Practice Question
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 developer is building a serverless application that uses Amazon S3 event notifications to trigger an AWS Lambda function for thumbnail generation. The developer wants to ensure that duplicate S3 events do not cause the same image to be processed multiple times. Which approach should the developer implement to ensure idempotent processing?
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
Store the object key and event ID in a DynamoDB table and check for duplicates before processing
Option A is correct because storing the S3 object key and event ID in a DynamoDB table with a TTL attribute allows the Lambda function to perform a conditional write (or check for an existing item) before processing. This ensures that even if duplicate S3 events are delivered (e.g., due to S3's at-least-once delivery guarantee), the same image is only processed once, achieving idempotency.
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.
- ✓
Store the object key and event ID in a DynamoDB table and check for duplicates before processing
Why this is correct
By recording processed object keys in DynamoDB and checking for existing records, the function can skip duplicate events, ensuring each object is processed only once.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Set the Lambda function's concurrency to 1 to prevent concurrent executions
Why it's wrong here
Limiting concurrency does not prevent duplicate events; it only ensures that only one invocation runs at a time, but duplicate events can still arrive and be processed sequentially.
- ✗
Use an Amazon SQS FIFO queue as the event destination
Why it's wrong here
S3 event notifications cannot be sent to FIFO queues; only standard queues are supported.
- ✗
Enable S3 event notification filtering based on object size
Why it's wrong here
Filtering based on object size controls which objects trigger events, but does not prevent duplicates for objects that match the filter.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume S3 event notifications are exactly-once, but the exam tests that they are at-least-once, requiring explicit idempotency handling via an external store like DynamoDB.
Detailed technical explanation
How to think about this question
Under the hood, S3 event notifications are delivered on an at-least-once basis, meaning the same event can be sent multiple times due to retries or internal replication. DynamoDB's conditional write with a unique constraint (using the event ID or a composite key of bucket+key+event ID) ensures that only the first write succeeds, and subsequent duplicates are ignored. In practice, you should also set a TTL on the DynamoDB item to automatically clean up old entries, preventing unbounded table growth.
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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: Store the object key and event ID in a DynamoDB table and check for duplicates before processing — Option A is correct because storing the S3 object key and event ID in a DynamoDB table with a TTL attribute allows the Lambda function to perform a conditional write (or check for an existing item) before processing. This ensures that even if duplicate S3 events are delivered (e.g., due to S3's at-least-once delivery guarantee), the same image is only processed once, achieving idempotency.
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: Jun 11, 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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