- A
Make the Lambda function idempotent by checking if the object has already been processed using a DynamoDB table.
Idempotency ensures that duplicate events do not cause duplicate processing.
- B
Use an SQS FIFO queue as the event destination and enable content-based deduplication.
Why wrong: S3 cannot send events to FIFO queues.
- C
Enable S3 bucket replication to another bucket and trigger Lambda from the replica.
Why wrong: Replication does not prevent duplicate events.
- D
Enable S3 bucket versioning and use 's3:ObjectCreated:Put' events.
Why wrong: Versioning does not eliminate duplicate events.
Question 132 of 1,616
How to Make S3-Triggered Lambda Idempotent Using DynamoDB
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 designing a system where an S3 bucket receives uploads, and each upload triggers a Lambda function to process the file. The processed output is stored in another S3 bucket. The developer notices that sometimes the same file is processed multiple times. How can this be prevented?
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
✓
Make the Lambda function idempotent by checking if the object has already been processed using a DynamoDB table.
Option A is correct because making the Lambda function idempotent using a DynamoDB table ensures that even if the same S3 event is delivered multiple times (due to at-least-once delivery semantics), the function checks a unique identifier (e.g., object key and ETag) in DynamoDB before processing. If the record exists, the function skips processing, preventing duplicate work. This directly addresses the root cause: S3 event notifications are delivered at least once, and Lambda may be invoked concurrently for the same object.
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.
- ✓
Make the Lambda function idempotent by checking if the object has already been processed using a DynamoDB table.
Why this is correct
Idempotency ensures that duplicate events do not cause duplicate processing.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use an SQS FIFO queue as the event destination and enable content-based deduplication.
Why it's wrong here
S3 cannot send events to FIFO queues.
- ✗
Enable S3 bucket replication to another bucket and trigger Lambda from the replica.
Why it's wrong here
Replication does not prevent duplicate events.
- ✗
Enable S3 bucket versioning and use 's3:ObjectCreated:Put' events.
Why it's wrong here
Versioning does not eliminate duplicate events.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that SQS FIFO queues can be directly integrated with S3 event notifications, but S3 only supports standard queues, making Option B an invalid configuration.
Detailed technical explanation
How to think about this question
S3 event notifications are delivered on an at-least-once basis, meaning Lambda may receive the same event multiple times due to retries or internal S3 replication delays. Using DynamoDB with a conditional write (e.g., PutItem with ConditionExpression: attribute_not_exists(PK)) provides a strongly consistent check that atomically ensures only the first invocation processes the file. This pattern is also resilient to concurrent invocations because DynamoDB’s conditional writes fail if the item already exists, preventing race conditions.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Development with AWS Services — study guide chapter
Learn the concepts, then practise the questions
- →
Development with AWS Services practice questions
Targeted practice on this topic area only
- →
All DVA-C02 questions
1,616 questions across all exam domains
- →
AWS Certified Developer Associate DVA-C02 study guide
Full concept coverage aligned to exam objectives
- →
DVA-C02 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related DVA-C02 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Development with AWS Services practice questions
Practise DVA-C02 questions linked to Development with AWS Services.
Security practice questions
Practise DVA-C02 questions linked to Security.
Deployment practice questions
Practise DVA-C02 questions linked to Deployment.
Troubleshooting and Optimization practice questions
Practise DVA-C02 questions linked to Troubleshooting and Optimization.
DVA-C02 fundamentals practice questions
Practise DVA-C02 questions linked to DVA-C02 fundamentals.
DVA-C02 scenario practice questions
Practise DVA-C02 questions linked to DVA-C02 scenario.
DVA-C02 troubleshooting practice questions
Practise DVA-C02 questions linked to DVA-C02 troubleshooting.
Practice this exam
Start a free DVA-C02 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: Make the Lambda function idempotent by checking if the object has already been processed using a DynamoDB table. — Option A is correct because making the Lambda function idempotent using a DynamoDB table ensures that even if the same S3 event is delivered multiple times (due to at-least-once delivery semantics), the function checks a unique identifier (e.g., object key and ETag) in DynamoDB before processing. If the record exists, the function skips processing, preventing duplicate work. This directly addresses the root cause: S3 event notifications are delivered at least once, and Lambda may be invoked concurrently for the same object.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on DVA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer is using AWS Lambda to process files uploaded to an S3 bucket. The Lambda function is triggered by S3 events. The developer notices that the function sometimes processes the same file multiple times. Which TWO steps should the developer take to make the processing idempotent? (Choose TWO.)
medium- ✓ A.Check if the file has already been processed by storing a marker in DynamoDB.
- ✓ B.Use conditional writes in DynamoDB to ensure that updates are idempotent.
- C.Reduce the S3 event batch size in the Lambda trigger.
- D.Increase the Lambda function's timeout.
- E.Enable S3 versioning on the bucket.
Why A: Option A is correct because storing a marker in DynamoDB (e.g., a record with the S3 object key as the partition key) allows the Lambda function to check if a file has already been processed before performing the work. This ensures that even if the same S3 event is delivered multiple times (due to retries or duplicate notifications), the function will skip reprocessing, making the operation idempotent.
Keep practising
More DVA-C02 practice questions
- A developer is troubleshooting an AWS Lambda function that is triggered by an S3 event. The function occasionally fails…
- A developer needs to call AWS APIs from application code running on EC2. Which credential source should the AWS SDK use…
- A developer needs to allow an IAM user in a different AWS account to assume a role in the developer's account. The role…
- A developer needs to grant an IAM role in Account B read-only access to objects in an S3 bucket in Account A. The bucket…
- An API Gateway HTTP API should allow access only to users authenticated by an external OIDC provider. Which authorizer t…
- A developer needs to allow an EC2 instance to read from a DynamoDB table. Which is the best practice to grant permission…
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.