How to Throttle Third-Party API Calls in Serverless Architecture?

DVA-C02 By islever Editorial Last updated

Short answer

B Configure the REST API in API Gateway to write the requests directly into an Amazon Simple Queue Service (Amazon SQS) queue. Configure the Lambda function with a reserved concurrency equal to the third-party stock application's threshold. Set Lambda function to process the messages from the SQS queue.

Question

A company has built a serverless application for its ecommerce website. The application includes a REST API in Amazon API Gateway that invokes an AWS Lambda function. The Lambda function processes data and stores the data in Amazon DynamoDB table. The Lambda function calls a third-party stock application API to process the order. After the ordered is processed, the Lambda function returns an HTTP 200 status code with no body to the client. During peak usage when the API calls exceeds a certain threshold, the third-party stock application sometimes fails to process the data and responds with error messages. The company needs a solution that will not overwhelm the third-party stock application. Which solution will meet these requirements?
  1. Configure the REST API in API Gateway to write the requests directly into DynamoDB. Configure a DynamoDB intrinsic function to perform the transformation. Set up a DynamoDB stream to call the third-party stock application API with each new row. Delete the Lambda function.
  2. Configure the REST API in API Gateway to write the requests directly into an Amazon Simple Queue Service (Amazon SQS) queue. Configure the Lambda function with a reserved concurrency equal to the third-party stock application's threshold. Set Lambda function to process the messages from the SQS queue. Correct Answer
  3. Configure the REST API in API Gateway to write the requests directly into an Amazon Simple Notification Service (Amazon SNS) topic. Configure the Lambda function with a provisioned concurrency equal to the third-party stock application's threshold. Set the Lambda function to process the messages from the SNS topic.
  4. Configure the REST API in API Gateway to write the requests directly into Amazon Athena. Configure the transformation of the data by using SQL with multiple query result locations set up to point to the DynamoDB table and the third-party stock fulfilment application API. Delete the Lambda function.

Key Takeaways

Evaluates your understanding of event-driven buffering and concurrency controls to prevent downstream service overload, often tricked by confusing throttling mechanisms with capacity provisioning.

This scenario tests decoupling API Gateway from direct Lambda execution using Amazon SQS to manage traffic spikes and protect external endpoints. The community unanimously agrees that pairing an SQS buffer with Lambda reserved concurrency is the optimal solution for rate-limiting.

Common mistake: Option C is frequently selected due to its use of SNS, but provisioned concurrency only guarantees warm instances rather than actively throttling invocation rates, making it ineffective for preventing API overload.

Expert Analysis

Why the Answer Is Correct

Using Amazon SQS as a buffer between API Gateway and Lambda effectively absorbs traffic spikes while maintaining system stability. Configuring reserved concurrency on the Lambda function strictly caps the number of simultaneous executions to match the third-party API's safe threshold. This architecture ensures requests are processed at a controlled pace, preventing timeouts or errors from the external service.

Why the Other Options Are Wrong

Option A relies on DynamoDB streams, which lack native concurrency throttling and would still trigger uncontrolled Lambda invocations during peak loads. Option C utilizes SNS with provisioned concurrency, but provisioned concurrency reserves capacity rather than enforcing rate limits, failing to address the overload requirement. Option D incorrectly applies Athena, an analytical query service, to real-time transactional workflows, introducing unacceptable latency and architectural mismatch.

Community Comment Notes

Candidates overwhelmingly validate option B as the industry-standard pattern for this certification objective. Contributors emphasize the decoupled flow where API Gateway writes to SQS, allowing Lambda to poll and process messages safely. Multiple users note that this exact configuration aligns with AWS best practices for handling unpredictable traffic and external dependency limits.

Official Reference

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Exam Strategy

When a question emphasizes protecting third-party APIs or managing peak traffic, prioritize message queuing solutions paired with explicit concurrency limits. Always distinguish between reserved concurrency, which actively throttles invocations, and provisioned concurrency, which merely pre-warms capacity without controlling throughput.

Community Votes

B
100%

100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 4

  1. tgv 👍 11
    B should do it: API Gateway --> SQS <-- Lambda poll
  2. CrescentShared 👍 5 Answered B
    no doubt.
  3. seetpt 👍 2 Answered B
    B is right
  4. 65703c1 👍 1 Answered B
    B is the correct answer.

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