SAP-C02 Design for New Solutions Practice Question
A solutions architect is designing a new serverless application using AWS Lambda for business logic, Amazon API Gateway for RESTful APIs, and Amazon DynamoDB for data storage. The application will experience unpredictable traffic spikes. What is the MOST cost-effective way to handle concurrency and scaling?
⚠ Common exam trap
Many candidates confuse provisioned concurrency (which reduces latency but adds cost) with reserved concurrency (which controls scaling and cost), or they mistakenly think DynamoDB auto scaling or API Gateway throttling directly manages Lambda concurrency.
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
✓
Use Lambda reserved concurrency to set a limit on concurrent executions.
Lambda reserved concurrency sets a hard limit on the number of concurrent executions for a function, preventing runaway scaling and controlling costs during unpredictable traffic spikes. It ensures that the function does not consume more concurrency than allocated, which avoids excessive DynamoDB read/write capacity usage and keeps costs predictable without needing to pre-warm instances.
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 Lambda provisioned concurrency to pre-warm instances.
Why it's wrong here
Provisioned concurrency adds cost and is not needed for unpredictable spikes; it's for latency-sensitive applications.
- ✓
Use Lambda reserved concurrency to set a limit on concurrent executions.
Why this is correct
Reserved concurrency controls the maximum number of concurrent Lambda invocations, preventing excessive scaling and cost.
- ✗
Configure DynamoDB auto scaling to handle traffic spikes.
Why it's wrong here
DynamoDB auto scaling manages read/write capacity, not Lambda concurrency.
- ✗
Set a usage plan in API Gateway with a throttling limit.
Why it's wrong here
API Gateway throttling limits API requests but does not directly control Lambda concurrency.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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