- A
Configure a Dead Letter Queue (DLQ) to capture failed messages.
Why wrong: DLQ stores messages after max retries, not related to at-least-once.
- B
Enable long polling on the SQS queue.
Why wrong: Long polling reduces empty responses but does not guarantee at-least-once processing.
- C
Use a FIFO queue to ensure exactly-once processing.
Why wrong: FIFO provides exactly-once, not at-least-once.
- D
Set the SQS queue's visibility timeout to be greater than the Lambda function's timeout.
If the function times out, the message becomes visible again, ensuring retry.
- E
Use the SQS DeleteMessage API inside the Lambda function only after successful processing.
Deleting only after success ensures message is not lost before processing.
Question 794 of 1,616
Ensure At-Least-Once Processing with SQS and Lambda
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 designing a highly available application using Amazon SQS and AWS Lambda. Which TWO strategies should the developer implement to ensure that messages are processed at least once? (Choose TWO.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"least"Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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
✓
Set the SQS queue's visibility timeout to be greater than the Lambda function's timeout.
Option D is correct because setting the SQS queue's visibility timeout to be greater than the Lambda function's timeout ensures that if the Lambda function fails or times out, the message becomes visible again in the queue after the visibility timeout expires, allowing another consumer to retry processing. This prevents messages from being lost due to processing failures, supporting at-least-once processing. Option E is correct because calling the SQS DeleteMessage API only after successful processing ensures that the message is not removed from the queue until it has been fully and correctly handled, so if processing fails, the message remains available for retry.
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.
- ✗
Configure a Dead Letter Queue (DLQ) to capture failed messages.
Why it's wrong here
DLQ stores messages after max retries, not related to at-least-once.
- ✗
Enable long polling on the SQS queue.
Why it's wrong here
Long polling reduces empty responses but does not guarantee at-least-once processing.
- ✗
Use a FIFO queue to ensure exactly-once processing.
Why it's wrong here
FIFO provides exactly-once, not at-least-once.
- ✓
Set the SQS queue's visibility timeout to be greater than the Lambda function's timeout.
Why this is correct
If the function times out, the message becomes visible again, ensuring retry.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Use the SQS DeleteMessage API inside the Lambda function only after successful processing.
Why this is correct
Deleting only after success ensures message is not lost before processing.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the purpose of a Dead Letter Queue (DLQ) as a mechanism for ensuring at-least-once processing, when in fact it is for isolating messages that have exhausted retries, not for guaranteeing delivery.
Detailed technical explanation
How to think about this question
Under the hood, SQS uses a visibility timeout mechanism to control message consumption: when a consumer receives a message, it becomes hidden from other consumers for the duration of the visibility timeout. If the consumer does not delete the message within that period, the message becomes visible again, enabling retries. In AWS Lambda integrations, the Lambda function's timeout must be shorter than the SQS visibility timeout to allow the message to reappear if the function fails, ensuring at-least-once delivery. A real-world scenario is processing financial transactions where a failure mid-processing must not lose the message; the combination of a longer visibility timeout and explicit deletion after success guarantees the message is retried until successful.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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.
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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: Set the SQS queue's visibility timeout to be greater than the Lambda function's timeout. — Option D is correct because setting the SQS queue's visibility timeout to be greater than the Lambda function's timeout ensures that if the Lambda function fails or times out, the message becomes visible again in the queue after the visibility timeout expires, allowing another consumer to retry processing. This prevents messages from being lost due to processing failures, supporting at-least-once processing. Option E is correct because calling the SQS DeleteMessage API only after successful processing ensures that the message is not removed from the queue until it has been fully and correctly handled, so if processing fails, the message remains available for retry.
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: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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
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