Jeff’s Note #
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 how to efficiently test serverless workflows locally without invoking real AWS services. In production, this is about knowing exactly which tooling supports mocking service integrations versus running only Lambda functions. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
DataStream Solutions is building an automated image recognition pipeline using AWS Step Functions. The pipeline orchestrates multiple AWS Lambda functions to preprocess images, train machine learning models, and store results. Image metadata flows into the pipeline through an Amazon Simple Queue Service (Amazon SQS) queue, while trained models are saved to an Amazon S3 bucket.
The development team needs a way to run and test the entire Step Functions workflow locally on their laptops without actually invoking Amazon SQS or Amazon S3 services. This will speed up iterative testing during development cycles.
The Requirement: #
Identify the solution that allows local execution and testing of the Step Functions workflow, including the Lambda functions, but avoids integration calls to real AWS managed services such as SQS and S3.
The Options #
- A) Use the Amazon CodeGuru Profiler to analyze the Lambda functions used in the AWS Step Functions pipeline.
- B) Use the AWS Step Functions Local Docker image to run and locally test the Lambda functions.
- C) Use the AWS Serverless Application Model (AWS SAM) CLI to run and locally test the Lambda functions.
- D) Use AWS Step Functions Local with mocked service integrations.
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Correct Answer #
D
Quick Insight: The Developer Imperative #
For a developer, local testing of Step Functions workflows that involve service integrations requires mock support. AWS Step Functions Local supports simulating state machines and mocking Amazon SQS, Amazon S3, and other service calls, making it the best choice here.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Option D
The Winning Logic #
AWS Step Functions Local is a downloadable runtime environment that perfectly emulates state machines on a developer’s local machine. Crucially, it has a feature to mock AWS service integrations, such as calls to Amazon SQS queues and Amazon S3 buckets. This allows developers to run the full Step Functions state machine end-to-end without triggering real AWS service endpoints — accelerating debugging and iteration cycles.
- The question specifically requires avoiding calls to Amazon SQS and Amazon S3, and Step Functions Local’s mocking capability meets this criterion.
- Local testing must include Lambda functions as part of the workflow, not just isolated Lambda invocations. Step Functions Local runs the entire orchestration engine locally.
The Trap (Distractor Analysis): #
- Option A (Amazon CodeGuru Profiler): This tool helps analyze runtime performance and identify bottlenecks in Lambda functions, but it doesn’t provide local workflow execution or mock service integrations. It is not a local testing environment.
- Option B (Step Functions Local Docker image to run Lambda functions): Step Functions Local by itself can simulate state machines, but running Lambda functions locally through it without mocks generally requires actual Lambda deployments or service calls. It does not fully mock integrated AWS services without additional setup.
- Option C (AWS SAM CLI): SAM CLI is ideal for local testing of individual Lambda functions and their events but does not run Step Functions workflows natively nor mock integrated service calls in the Step Functions context.
- Option D is specifically the only option designed to allow local Step Functions execution with mocked service integrations, perfectly fitting the use case.
The Technical Blueprint #
Relevant CLI snippet to start Step Functions Local with mocks: #
java -jar StepFunctionsLocal.jar --lambda-endpoint http://localhost:3001 --services-mock-config mocks.json
Example mocks.json might mock “sqs” and “s3” calls to bypass actual AWS calls during workflow execution.
The Comparative Analysis #
| Option | API Complexity | Performance | Use Case |
|---|---|---|---|
| A | N/A | Code profiling only | Performance analysis of Lambda only |
| B | Medium (Step Functions) | Runs state machine locally | Local Step Functions but limited service mocks |
| C | Low (Lambda only) | Runs single Lambda locally | Lambda unit testing only |
| D | Medium-High | Full workflow local + mocks | Local Step Functions with integrated service mocks |
Real-World Application (Practitioner Insight) #
Exam Rule #
For the exam, always pick Step Functions Local with mocked integrations when you see the requirement of local testing complex workflows involving managed AWS services without actual network calls.
Real World #
In actual development, teams often combine SAM CLI for Lambda functions and Step Functions Local with mocks to cover both isolated function testing and end-to-end workflow testing locally before deployment.
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS DVA-C02 exam.