The answer is to use Amazon SQS to buffer the requests and set a Lambda reserved concurrency to limit the processing rate. This works because SQS acts as a durable buffer that decouples the S3 trigger from the Lambda function, allowing you to control the invocation rate by setting reserved concurrency on the function to a value that ensures no more than 10 concurrent executions per second, directly matching the external API’s rate limit. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of throttling patterns in serverless architectures, often appearing as a trap where candidates mistakenly choose increasing timeout or SNS, which lack rate control. A key memory tip is to think of reserved concurrency as a “speed limiter” and SQS as the “holding lane” — together they prevent your Lambda from overwhelming the external API.
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 new serverless application using AWS Lambda. The function must process a file uploaded to S3 and then send a notification to an external API. The external API has a rate limit of 10 requests per second. Which approach should they use to handle throttling?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Amazon SQS to buffer the requests and set a Lambda reserved concurrency to limit the processing rate
Option D is correct because using SQS as a dead-letter queue with a Lambda reserved concurrency and a throttle can control the rate. Option A is wrong because increasing timeout does not handle rate limiting. Option B is wrong because SNS does not provide rate control. Option C is wrong because Lambda destination on failure alone does not throttle.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 Amazon SQS to buffer the requests and set a Lambda reserved concurrency to limit the processing rate
Why this is correct
SQS can buffer requests and Lambda reserved concurrency can limit concurrency, effectively throttling the rate.
Related concept
Static NAT maps one inside address to one outside address.
✗
Increase the Lambda function timeout and retry on failure
Why it's wrong here
Increasing timeout does not control the rate of API calls.
✗
Configure a Lambda function destination on failure to reprocess
Why it's wrong here
This only handles failures, not rate control.
✗
Use Amazon SNS to fan out the notification to multiple Lambda functions
Why it's wrong here
SNS does not provide rate limiting.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
Design for New Solutions — This question tests Design for New Solutions — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use Amazon SQS to buffer the requests and set a Lambda reserved concurrency to limit the processing rate — Option D is correct because using SQS as a dead-letter queue with a Lambda reserved concurrency and a throttle can control the rate. Option A is wrong because increasing timeout does not handle rate limiting. Option B is wrong because SNS does not provide rate control. Option C is wrong because Lambda destination on failure alone does not throttle.
What should I do if I get this SAP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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