AWS DVA-C02 Drill: Serverless REST APIs - Cost-Effective Endpoint Design

Jeff’s Note

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Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.

For AWS DVA-C02 candidates, the confusion often lies in choosing the best deployment model for minimal traffic without overspending. In production, this boils down to knowing exactly when to leverage serverless architectures with built-in caching to reduce operational overhead and cost. Let’s drill down.

The Certification Drill (Simulated Question)

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Scenario

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InnovaWeather Inc., a startup focused on smart building solutions, needs to develop a proof of concept for a web-based service that shows live weather forecasts for its regional offices. The company plans to provide a REST API endpoint that internal clients can call to fetch this data. Since the project is in early experimental stages, traffic to the backend will be minimal and irregular. To keep backend costs low and optimize performance, the development team wants to use AWS managed caching features wherever possible to avoid excessive API calls to external weather services.

The Requirement

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Design and implement the REST API endpoint in the most cost-effective way during this proof of concept phase, while taking advantage of AWS caching capabilities.

The Options

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• A) Package the application as a container image, deploy it on Amazon Elastic Kubernetes Service (Amazon EKS), and expose the API using Amazon API Gateway with caching enabled.
• B) Write an AWS Lambda function packaged using AWS Serverless Application Model (AWS SAM), expose it with Amazon API Gateway, and enable API Gateway caching.
• C) Package the application as a container image, deploy it on Amazon Elastic Container Service (Amazon ECS), and expose the API endpoint through Amazon API Gateway.
• D) Develop a microservices app, deploy it on AWS Elastic Beanstalk, and front the app with an Application Load Balancer (ALB) integrated with AWS Lambda to handle dynamic processing.

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Correct Answer

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B

Quick Insight: The Developer Imperative

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Using Lambda deployed with SAM and fronted by API Gateway provides the lowest operational overhead and pricing footprint in low-traffic POCs. API Gateway’s built-in caching can be enabled with minimal effort, reducing redundant weather service calls without provisioning or managing servers.

Container orchestration (EKS or ECS) incurs higher baseline cost and management complexity. Elastic Beanstalk with ALB plus Lambda is overkill for a simple POC REST endpoint.

Content Locked: The Expert Analysis

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You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?

The Expert’s Analysis

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Correct Answer

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Option B

The Winning Logic

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Option B leverages AWS Lambda’s serverless pricing model, which matches perfectly for a proof-of-concept workload with minimal traffic—there are no charges when the function isn’t invoked. Wrapping the Lambda function with AWS SAM accelerates build/deploy cycles drastically, aligning with developer productivity goals.

Amazon API Gateway adds the RESTful endpoint layer and offers native caching capabilities, which can be toggled easily. This reduces downstream invocations to the external backend weather service, cutting data transfer costs and latency.

• Lambda and API Gateway together provide a fully managed, scalable, and cost-efficient stack.
• Minimal operational overhead—no cluster or server management.
• Fine-grained caching control at the API Gateway level.

The Trap (Distractor Analysis):

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• Why not A? EKS requires always-on EC2 nodes even when traffic is low, inflating cost. Operational complexity and cluster maintenance overhead see no return for a POC with sparse usage.
• Why not C? ECS simplifies container orchestration versus EKS but still entails managing at least a few EC2 instances or Fargate tasks, which incur continuous charges. No inherent caching at ECS level—relies on API Gateway caching only.
• Why not D? Elastic Beanstalk abstracts infrastructure but is heavier than necessary, and integrating ALB with Lambda here complicates routing. More moving parts increase costs, complexity, and deployment time, not justified for a simple REST endpoint.

The Technical Blueprint

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B) For Developer (Code Snippet):

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Enable API Gateway caching with AWS CLI:

aws apigateway update-stage \
  --rest-api-id <api-id> \
  --stage-name prod \
  --patch-operations op=replace,path=/cacheClusterEnabled,value=true

# Additionally configure cache TTL (in seconds)
aws apigateway update-stage \
  --rest-api-id <api-id> \
  --stage-name prod \
  --patch-operations op=replace,path=/cacheClusterSize,value="0.5"

Sample AWS SAM function snippet for Lambda + API Gateway:

Resources:
  WeatherFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: app.lambda_handler
      Runtime: python3.9
      Events:
        WeatherApi:
          Type: Api
          Properties:
            Path: /weather
            Method: get
            CacheClusterEnabled: true
            CacheClusterSize: "0.5"

The Comparative Analysis

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Real-World Application (Practitioner Insight)

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Exam Rule

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For the exam, always pick AWS Lambda + API Gateway when you see low traffic, event-driven REST endpoints with caching requirements.

Real World

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In a real production environment, developers might move to ECS or EKS once traffic scales, or add CDN caching with CloudFront. But for a proof of concept or small testing workloads, Lambda’s pay-per-use model is unbeatable.

(CTA) Stop Guessing, Start Mastering

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Disclaimer

This is a study note based on simulated scenarios for the AWS DVA-C02 exam.