AWS DVA-C02 Drill: API Gateway & Lambda Integration - Correct Response Format

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 DVA-C02 candidates, the confusion often lies in knowing what API Gateway requires in Lambda responses to avoid gateway errors like HTTP 502. In production, this is about knowing exactly how your Lambda function must signal success or failure back to API Gateway in the right JSON structure and with proper headers. Let’s drill down.”

The Certification Drill (Simulated Question)

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Scenario

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Imagine you are the lead developer at BlueWave Solutions, a company building a serverless travel booking app. Your team created an Amazon API Gateway endpoint that triggers a Lambda function to process booking requests. However, when calling the API, users encounter a “502 Bad Gateway” error. The API Gateway logs show a message: “Method completed with status: 502.”

The Requirement

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Identify the correct fix that resolves this API Gateway 502 error by adjusting the integration between API Gateway and Lambda.

The Options

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• A) Change the API Gateway’s HTTP endpoint to HTTPS.
• B) Change the format of the payload sent from the client to the API Gateway.
• C) Change the Lambda function’s response format to comply with API Gateway’s expected structure.
• D) Change or remove the authorization header in the API call that accesses the Lambda function.

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Correct Answer

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C

Quick Insight: The Developer Imperative

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When integrating API Gateway with Lambda via proxy integration, API Gateway expects the Lambda function to return a properly structured JSON response with statusCode, headers, and body fields. If the Lambda response does not align with this format, API Gateway will throw a 502 error indicating an invalid response. This is a common stumbling block for developers learning API Gateway integration.

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 C

The Winning Logic

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The key to resolving a 502 Bad Gateway error when using API Gateway with Lambda (especially with Lambda proxy integration) is ensuring the Lambda function’s output matches the API Gateway’s expected response JSON schema. This schema generally looks like:

{
    "statusCode": 200,
    "headers": { "Content-Type": "application/json" },
    "body": "{\"key\": \"value\"}"
}

API Gateway requires this structured response so it can properly interpret status codes, set HTTP headers, and send the body back to the client. If the Lambda function returns raw JSON without these fields or returns data in the wrong format, API Gateway treats it as an invalid response and returns a 502 error.

By changing the Lambda function to return this formatted response, you give proper instructions to API Gateway on how to construct the HTTP response, resolving the 502 error.

Developer Perspective:

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• Use SDK or JSON serialization to wrap your result.
• Ensure the body is a string, often JSON-stringified.
• Include a numeric statusCode to represent HTTP status.
• Specify any headers if needed.

The Trap (Distractor Analysis):

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• Why not A? Changing HTTP to HTTPS is unrelated; API Gateway supports both, and the 502 error is a backend integration problem, not a transport protocol issue.

• Why not B? The payload sent to API Gateway might cause validation errors but not a 502 gateway error. Incorrect request format often leads to 4XX errors, not 502 errors from API Gateway.

• Why not D? Authorization header issues cause 401 or 403 errors, not 502. Also, removing or changing headers unrelated to the integration response won’t fix response format errors.

The Technical Blueprint

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# Example Python Lambda function response expected by API Gateway proxy integration

def lambda_handler(event, context):
    response = {
        "statusCode": 200,
        "headers": {
            "Content-Type": "application/json"
        },
        "body": '{"message": "Booking processed successfully"}'
    }
    return response

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 the option that ensures the Lambda response is properly structured when working with API Gateway proxy integration.

Real World

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In real projects, misformatted Lambda responses cause hours of debugging. Tools like AWS SAM CLI and local API Gateway emulators help developers test the exact response structure before deployment, saving time and headaches.

(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.