Question

A developer builds a REST API using API Gateway with a Lambda proxy integration (AWS_PROXY). When the Lambda function encounters a validation error, the developer wants API Gateway to return an HTTP 400 status with a custom JSON error body to the client. Currently, all responses—including handled errors—return HTTP 200. What is the correct way to make the function return a 400 status to the client?

Accepted Answer

Return a response object from the Lambda function with a 'statusCode' of 400 and a 'body' string containing the JSON error.

Answer

Configure a Method Response and Integration Response mapping template in API Gateway to convert the 200 into a 400.

Answer

Throw an unhandled exception in the Lambda function so API Gateway automatically maps it to a 400 status code.

Answer

Set the 'Content-Handling' property of the integration to CONVERT_TO_TEXT and add a 400 status to the method settings.