SAP-C02 API Gateway Throttling Practice Question
A company is using Amazon API Gateway to expose a REST API. The API backend is a Lambda function that queries an Amazon DynamoDB table. During peak hours, the API returns HTTP 429 (Too Many Requests) errors. What is the MOST cost-effective way to reduce these errors?
⚠ Common exam trap
Candidates often confuse the source of 429 errors. In API Gateway, 429 errors indicate throttling at the API Gateway level, not necessarily at the backend. Therefore, increasing backend capacity (Lambda concurrency or DynamoDB throughput) may not resolve the issue if the API Gateway limit is too low.
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
✓
Increase the throttling limits in API Gateway.
HTTP 429 errors from API Gateway indicate that the request rate is exceeding the configured throttling limits. Increasing the throttling limits allows more requests to pass through directly, and this is a cost-effective configuration change. Option A (API caching) can reduce backend load but does not address the throttling limit itself. Option B (DynamoDB auto-scaling) addresses DynamoDB capacity, not API Gateway throttling. Option D (Lambda reserved concurrency) addresses Lambda throttling, but the 429 is from API Gateway, not Lambda.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable API caching in API Gateway.
Why it's wrong here
API caching reduces the number of requests that reach the backend for cached responses, but the 429 error occurs at the API Gateway level due to throttling limits, not backend capacity. This does not directly resolve the throttling issue.
- ✗
Enable DynamoDB auto-scaling.
Why it's wrong here
DynamoDB auto-scaling adjusts read/write capacity based on usage, which helps if DynamoDB is throttling, but the 429 error originates from API Gateway, not DynamoDB. Not the direct solution.
- ✓
Increase the throttling limits in API Gateway.
Why this is correct
Increasing API Gateway throttling limits directly allows more requests to be processed before hitting the limit. This is the most cost-effective as it involves only a configuration change without additional infrastructure costs.
- ✗
Increase the reserved concurrency of the Lambda function.
Why it's wrong here
Increasing Lambda reserved concurrency ensures Lambda can handle more concurrent invocations, but the 429 error is from API Gateway exceeding its own limit, not from Lambda throttling. This would be more expensive and not address the root cause.
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 |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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