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Difficulty: HardAPI Development and Integration with Amazon API Gateway

A developer is building a serverless backend using Amazon API Gateway and AWS Lambda. The API Gateway REST API is configured with a Lambda custom (non-proxy) integration. When the client sends invalid input, the Lambda function throws an exception with the error message: `[ValidationFailed] User age is under the legal limit`. The developer wants API Gateway to return a `400 Bad Request` HTTP response with a custom JSON payload when this error occurs. Which configuration steps must the developer perform in API Gateway to achieve this?

  1. Configure a Method Response for the 400 status code. In the Integration Response, configure an entry with a Lambda Error Regex pattern set to `.*ValidationFailed.*`, map it to the 400 Method Response, and define a body mapping template to customize the returned JSON payload.Answer
  2. B
    Enable Lambda proxy integration, and configure an Integration Response with a Lambda Error Regex pattern set to `.*ValidationFailed.*` to map the exception to a 400 Method Response.
  3. C
    Configure a custom Lambda authorizer on the method to validate the input payload, and set the Gateway Response for 400 bad requests to transform the exception message.
  4. D
    Define the regex pattern `.*ValidationFailed.*` directly in the Method Response configuration, and map the matching pattern to the integration request body mapping template to mock the response without executing the Lambda function.

Answer

Configure a Method Response for the 400 status code, create an Integration Response with a Lambda Error Regex matching the error message (such as `.*ValidationFailed.*`), link it to the 400 Method Response, and define a body mapping template.
The correct answer correctly outlines the requirements for mapping Lambda errors to custom HTTP responses in a non-proxy (custom) integration. This involves: 1) Declaring the HTTP status code (400) in the Method Response. 2) Creating an Integration Response with a selection pattern regex (such as `.*ValidationFailed.*`) that matches the Lambda function's error message. 3) Specifying a VTL mapping template to shape the output payload returned to the client.

Step-by-Step Solution

1
Define the HTTP status code in the Method Response configuration.
The API Gateway Method is registered as capable of returning a 400 Bad Request status code to the client.
Before an Integration Response can map an output to a status code, that status code must first be declared in the Method Response.
2
Create an Integration Response entry and set the Lambda Error Regex selection pattern.
The selection pattern evaluates the `errorMessage` property of the JSON payload returned by Lambda (e.g. matching `.*ValidationFailed.*`).
API Gateway matches the regex pattern against the string returned in the Lambda error's `errorMessage` header or payload to select the correct integration response.
3
Associate the Integration Response entry with the 400 Method Response and define a body mapping template.
API Gateway transforms the Lambda error JSON (containing `errorMessage`, `errorType`, `stackTrace`) into the custom client-facing JSON structure.
This shapes the response payload to match client expectations, hiding internal stack traces and presenting a clean error format.

Key Concept

API Gateway integration and response mapping patterns for Lambda non-proxy integrations
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Topics

API Development and Integration with Amazon API Gateway

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