- A
The Lambda function is not deleting messages from the queue after successful processing, so they become visible again after the visibility timeout.
If the function does not delete the message from the queue, the message reappears after the visibility timeout expires, causing duplicate processing. FIFO queues do not automatically remove messages; the consumer must explicitly delete them.
- B
The Lambda function is configured with a batch size greater than 1, causing multiple messages to be processed at once and some to be duplicated.
Why wrong: Batch processing is supported but does not cause duplicates. All messages in a batch must be deleted individually. If one message fails, the entire batch is not deleted, but duplicates are not inherent.
- C
The SQS queue has a message retention period set too low, causing messages to be deleted automatically and re-queued.
Why wrong: Message retention period only controls how long a message stays in the queue before being deleted permanently. It does not cause duplicates.
- D
The Lambda function's execution role does not have permission to delete messages from the queue.
Why wrong: If the role lacks delete permission, the function will fail but will not cause duplicates; the message would become visible again after visibility timeout. However, this is less likely than the function simply not calling DeleteMessage for other reasons.
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 uses an Amazon SQS FIFO queue to process orders. The orders must be processed exactly once and in the order they are received. The developer uses an AWS Lambda function as the consumer. Despite using a FIFO queue, the developer notices that some orders are being processed more than once. What is the most likely cause of this behavior?
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 Lambda function is not deleting messages from the queue after successful processing, so they become visible again after the visibility timeout.
The most likely cause is that the Lambda function is not deleting messages from the SQS FIFO queue after successful processing. By default, Lambda does not automatically delete messages; it relies on the function code to call the `DeleteMessage` API. If the function fails to delete a message, it remains in the queue and becomes visible again after the visibility timeout expires, leading to duplicate processing even though the queue is FIFO.
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 Lambda function is not deleting messages from the queue after successful processing, so they become visible again after the visibility timeout.
Why this is correct
If the function does not delete the message from the queue, the message reappears after the visibility timeout expires, causing duplicate processing. FIFO queues do not automatically remove messages; the consumer must explicitly delete them.
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.
- ✗
The Lambda function is configured with a batch size greater than 1, causing multiple messages to be processed at once and some to be duplicated.
Why it's wrong here
Batch processing is supported but does not cause duplicates. All messages in a batch must be deleted individually. If one message fails, the entire batch is not deleted, but duplicates are not inherent.
- ✗
The SQS queue has a message retention period set too low, causing messages to be deleted automatically and re-queued.
Why it's wrong here
Message retention period only controls how long a message stays in the queue before being deleted permanently. It does not cause duplicates.
- ✗
The Lambda function's execution role does not have permission to delete messages from the queue.
Why it's wrong here
If the role lacks delete permission, the function will fail but will not cause duplicates; the message would become visible again after visibility timeout. However, this is less likely than the function simply not calling DeleteMessage for other reasons.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume FIFO queues guarantee exactly-once processing automatically, but they actually guarantee exactly-once delivery to the consumer, not exactly-once processing—the consumer must still delete the message to prevent reprocessing.
Detailed technical explanation
How to think about this question
Under the hood, Lambda integrates with SQS via event source mappings that poll the queue and invoke the function. The visibility timeout is a critical mechanism: when a message is received, it becomes hidden for the duration of the timeout, but if the function does not delete it, the message reappears after the timeout expires. In FIFO queues, the `ReceiveMessage` call uses a receive request attempt ID to prevent duplicates, but this does not protect against the consumer failing to delete the message. A real-world scenario is when a Lambda function crashes after processing but before calling `DeleteMessage`, causing the same order to be processed again.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: The Lambda function is not deleting messages from the queue after successful processing, so they become visible again after the visibility timeout. — The most likely cause is that the Lambda function is not deleting messages from the SQS FIFO queue after successful processing. By default, Lambda does not automatically delete messages; it relies on the function code to call the `DeleteMessage` API. If the function fails to delete a message, it remains in the queue and becomes visible again after the visibility timeout expires, leading to duplicate processing even though the queue is FIFO.
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.
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.
About these practice questions
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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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