You have an application that is hosted on an EC2 Instance. This application is part of a custom domain www.demo.com. The application has been changed to make calls to the API gateway. But the browser is not rendering the responses and Javascript errors are being seen in the developer console. What must be done to ensure that this issue can be resolved?

Answer options:

A.Make the application call a Lambda function instead.
B.There is an issue with the stage defined on the API gateway, hence define a new stage.
C.Make use of Cognito user pools.
D.Enable CORS for the API gateway.

Answer – D
This is given in the AWS Documentation.
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When your API`s resources receive requests from a domain other than the API`s own domain, you must enable cross-origin resource sharing (CORS) for selected methods on the resource. This amounts to having your API respond to the OPTIONS preflight request with at least the following CORS-required response headers:
Access-Control-Allow-Methods
Access-Control-Allow-Headers
Access-Control-Allow-Origin
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Option A is invalid because you should not make the architecture change, since this is not the underlying issue.
Option B is invalid because this is the problem with CORS and not the stage itself.
Option C is invalid because using Cognito user pools would add one more unnecessary layer of authentication which is not part of the question requirement.
For more information on CORS for API gateway, please refer to the below URL-
https://docs.aws.amazon.com/apigateway/latest/developerguide/how-to-cors.html