Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
A developer is troubleshooting an AWS Lambda function that is invoked from an Amazon S3 bucket via event notifications. The function processes images and stores metadata in Amazon DynamoDB. The developer notices that some images are being processed multiple times, resulting in duplicate entries in DynamoDB. The S3 event notification is configured to send events to the Lambda function with the 's3:ObjectCreated:*' event type. The function uses the 'uuid' library to generate a unique ID for each image upon processing. What is the most likely cause of the duplicate processing?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
S3 event notifications are delivered at least once, and the Lambda function is not idempotent.
S3 can send the same event multiple times. Without idempotency checks (e.g., using the S3 object key as the DynamoDB primary key), each event creates a new item, causing duplicates.
B
Distractor review
The Lambda function's concurrency is set too high, causing race conditions.
High concurrency can cause race conditions but not duplicate event delivery. Duplicate events originate from S3, not from concurrency.
C
Distractor review
The DynamoDB table does not have a primary key that prevents duplicates.
Even with a primary key, the UUID generated per invocation differs, so each duplicate event creates a new item. The real issue is lack of idempotency, not table schema.
D
Distractor review
The S3 bucket is configured with versioning, causing multiple object creation events.
Versioning can generate multiple events (e.g., PutObject and CopyObject) for the same object, but the most common cause of duplicate processing is the 'at least once' delivery of notifications.
Common exam trap
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.
Technical deep dive
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.
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.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A developer is building a REST API using Amazon API Gateway that will serve static content from an Amazon S3 bucket. The API should cache responses for frequently accessed objects to reduce latency. Which API Gateway feature should the developer enable?
Question 2
A developer is running a web application on multiple Amazon EC2 instances behind an Application Load Balancer (ALB). The application needs to store user session state that must be available across all instances. The session data is small and temporary but must survive individual instance failures. Which AWS service should the developer use to store this session state?
Question 3
A developer has an AWS Lambda function that processes messages from an Amazon SQS standard queue. The function is idempotent and currently has a batch size of 10. The developer wants to increase throughput and increases the batch size to 100. After the change, CloudWatch metrics show a significant increase in throttles and the queue backlog is growing. The function's reserved concurrency is set to 10. What is the most effective action to resolve the throttling and improve throughput?
Question 4
A developer is managing an application running on Amazon EC2 instances behind an Application Load Balancer. Users report that the application becomes unresponsive after several hours, and restarting the instance temporarily fixes the issue. The developer suspects a memory leak but cannot add custom instrumentation. Which AWS service can collect memory utilization metrics and help identify the memory leak with minimal configuration?
Question 5
A developer is building a serverless web application using AWS Lambda and Amazon DynamoDB. The application needs to perform complex aggregations on data stored in DynamoDB. Which AWS service should the developer use to perform these aggregations efficiently without reading all the data into Lambda?
Question 6
A developer has an Amazon S3 bucket containing private user documents. The application must generate a time-limited URL for users to download their own documents without requiring the users to have AWS credentials. Which solution should the developer use?
FAQ
Questions learners often ask
What does this DVA-C02 question test?
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: S3 event notifications are delivered at least once, and the Lambda function is not idempotent. — S3 event notifications are delivered on an 'at least once' basis, meaning the same event can be delivered multiple times. If the Lambda function is not idempotent (i.e., it does not check whether a record already exists before writing), duplicate events lead to duplicate processing. Option B is incorrect because concurrency does not cause duplicate events. Option C is incorrect because the UUID is generated each time, so even with a primary key, each duplication creates a new item with a different UUID. Option D is incorrect: while versioning can generate multiple events (e.g., PutObject and CopyObject), the primary cause is duplicate delivery of the same event.
What should I do if I get this DVA-C02 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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