- A
The Lambda function's reserved concurrency is set too high.
Why wrong: Reserved concurrency limits the maximum number of concurrent executions; it does not cause duplication.
- B
The SQS visibility timeout is too short for the Lambda function's execution time.
If the visibility timeout expires before Lambda finishes processing, the message becomes visible again and can be processed by another invocation.
- C
The SQS queue has a dead-letter queue configured.
Why wrong: A dead-letter queue is used for messages that fail processing, not for duplication.
- D
The Lambda function's batch size is set to more than 1.
Why wrong: Lambda processes messages in batches but each message is handled individually; batch size does not cause duplication.
Question 1,286 of 1,616
Why Lambda Processes SQS Messages Multiple Times and How to Fix It
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 using AWS Lambda functions that process events from Amazon SQS. The developer notices that some messages are being processed multiple times. What is the MOST likely cause of this issue?
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 SQS visibility timeout is too short for the Lambda function's execution time.
When an SQS message is processed by a Lambda function, the message becomes invisible to other consumers for the duration of the visibility timeout. If the Lambda function takes longer to process the message than the visibility timeout, SQS makes the message visible again and can deliver it to another consumer (or the same Lambda function in a new invocation), causing duplicate processing. This is the most likely cause of messages being processed multiple times.
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's reserved concurrency is set too high.
Why it's wrong here
Reserved concurrency limits the maximum number of concurrent executions; it does not cause duplication.
- ✓
The SQS visibility timeout is too short for the Lambda function's execution time.
Why this is correct
If the visibility timeout expires before Lambda finishes processing, the message becomes visible again and can be processed by another invocation.
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 SQS queue has a dead-letter queue configured.
Why it's wrong here
A dead-letter queue is used for messages that fail processing, not for duplication.
- ✗
The Lambda function's batch size is set to more than 1.
Why it's wrong here
Lambda processes messages in batches but each message is handled individually; batch size does not cause duplication.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse the visibility timeout with the Lambda function timeout or think that increasing concurrency or batch size causes duplicates, when in fact the visibility timeout directly controls the window for duplicate processing.
Detailed technical explanation
How to think about this question
The SQS visibility timeout is a timer that starts when a consumer receives a message; if the consumer does not delete the message before the timeout expires, SQS assumes the consumer failed and makes the message available for redelivery. Lambda’s integration with SQS uses long polling and automatically deletes messages from the queue only after the function successfully completes, so if the function execution time exceeds the visibility timeout, the message becomes visible again before deletion, leading to at-least-once delivery semantics and potential duplicates.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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 SQS visibility timeout is too short for the Lambda function's execution time. — When an SQS message is processed by a Lambda function, the message becomes invisible to other consumers for the duration of the visibility timeout. If the Lambda function takes longer to process the message than the visibility timeout, SQS makes the message visible again and can deliver it to another consumer (or the same Lambda function in a new invocation), causing duplicate processing. This is the most likely cause of messages being processed multiple times.
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.
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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.
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