API gateway and Lambda proxy integrations have been chosen to implement an application by a software engineer. The application is a data analysis tool that returns some statistical results when the HTTP endpoint is called. The Lambda needs to communicate with some back-end data services such as Keen.io. However, there are chances that error happens, such as wrong data requested, bad communications, etc. The Lambda is written using Java. Two exceptions may be returned which are BadRequestException and InternalErrorException. What should the software engineer do to map these two exceptions in the API gateway with proper HTTP return codes? For example, BadRequestException and InternalErrorException are mapped to HTTP return codes 400 and 500 respectively. Select 2.

Answer options:

A.Add the corresponding error codes (400 and 500) on the Integration Response in the API gateway.
B.Add the corresponding error codes (400 and 500) on the Method Response in the API gateway.
C.Put the mapping logic into Lambda itself so that when an exception happens, error codes are returned at the same time in a JSON body.
D.Add Integration Responses where regular expression patterns are set, such as BadRequest or InternalError. Associate them with HTTP status codes.
E.Add Method Responses where regular expression patterns are set, such as BadRequest or InternalError. Associate them with HTTP status codes 400 and 500.

Correct Answer – B, D
 
When an API gateway is established, there are four parts.
Method Request/Method Response mainly deals with API gateways. They are the API`s interface with the API`s frontend (a client), whereas Integration Request and Integration Response are the API`s interface with the backend. In this case, the backend is a Lambda.
For the mapping of exceptions that come from Lambda, Integration Response is the correct place to configure. However, the corresponding error code (400) on the method response should be created first. Otherwise, API Gateway throws an invalid configuration error response at runtime. Below is an example of mapping BadRequestException to HTTP return code 400:
Option A is incorrect: Because HTTP error codes are defined as firstly in Method Response instead of Integration Response.
Option B is CORRECT: Because HTTP error codes are defined as firstly in Method Response instead of Integration Response. (Same reason as A).
Option C is incorrect: Because Integration Response in API gateway should be used. Refer to https://docs.aws.amazon.com/apigateway/latest/developerguide/handle-errors-in-lambda-integration.html on “how to Handle Lambda Errors in API Gateway”.
Option D is CORRECT: Because BadRequest or InternalError should be mapped to 400 and 500 in Integration Response settings.
Option E is incorrect: Because Method Response is the interface with the frontend. It does not deal with how to map the response from Lambda/backend.