The correct choice is to use an SQS queue as a Lambda event source with reserved concurrency on the Lambda function. This configuration prevents message loss because SQS acts as a durable, highly available buffer that holds messages until they are successfully processed, while reserved concurrency guarantees that the Lambda function always has dedicated execution capacity, preventing it from being throttled during unpredictable traffic spikes. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how Lambda’s synchronous invocation model interacts with SQS’s polling behavior—a common trap is assuming that simply adding a dead-letter queue solves the problem, but without reserved concurrency, throttled invocations can still cause messages to expire or be redirected prematurely. Remember the memory tip: “Reserve your concurrency to keep the queue in your favor.”
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 company is designing a serverless event-driven architecture using AWS Lambda, Amazon SQS, and Amazon DynamoDB. The Lambda function processes messages from an SQS queue and writes to DynamoDB. The company expects unpredictable traffic spikes and must ensure that messages are not lost. Which configuration should the company use to meet these requirements?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use an SQS queue as a Lambda event source with reserved concurrency on the Lambda function
Option A is correct because using an SQS queue as a Lambda event source with reserved concurrency ensures that messages are not lost during traffic spikes. SQS acts as a durable buffer, and reserved concurrency prevents the Lambda function from being throttled, which would otherwise cause messages to remain in the queue or be sent to a dead-letter queue. This combination guarantees that every message is processed without loss, even under unpredictable load.
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.
✓
Use an SQS queue as a Lambda event source with reserved concurrency on the Lambda function
Why this is correct
Reserved concurrency prevents throttling, and SQS acts as a buffer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable DynamoDB Accelerator (DAX) for the Lambda function
Why it's wrong here
DAX is a cache, not relevant to message processing.
✗
Provisioned Concurrency on the Lambda function
Why it's wrong here
Provisioned Concurrency is for cold starts, not for preventing message loss.
✗
Increase the SQS queue visibility timeout and retention period
Why it's wrong here
This does not prevent message loss during throttling.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse Provisioned Concurrency (which reduces cold starts) with reserved concurrency (which guarantees processing capacity), and overlook that SQS alone cannot prevent message loss if Lambda is throttled.
Detailed technical explanation
How to think about this question
When Lambda polls an SQS queue, it uses long polling and processes messages in batches. If the function is throttled (due to hitting the account-level concurrency limit), unprocessed messages remain in the queue but can become stale or be sent to a dead-letter queue after the visibility timeout expires. Reserved concurrency allocates a dedicated pool of concurrency for the function, ensuring that Lambda can always scale to process incoming messages, even during traffic spikes. This is critical because SQS does not automatically retry throttled invocations; it relies on the visibility timeout to make messages visible again, which can lead to duplicate processing or message loss if not configured correctly.
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.
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.
Design for New Solutions — This question tests Design for New Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use an SQS queue as a Lambda event source with reserved concurrency on the Lambda function — Option A is correct because using an SQS queue as a Lambda event source with reserved concurrency ensures that messages are not lost during traffic spikes. SQS acts as a durable buffer, and reserved concurrency prevents the Lambda function from being throttled, which would otherwise cause messages to remain in the queue or be sent to a dead-letter queue. This combination guarantees that every message is processed without loss, even under unpredictable load.
What should I do if I get this SAP-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.
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Question Discussion
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