Can't access API with Lambda and API Gateway

Question

I have an aws lambda function that returns the following response:

var responseBody = { cost: price };
var response = {
   statusCode: 200,
   headers: {
          "Access-Control-Allow-Origin": "*"
     },
    body: JSON.stringify(responseBody),
    isBase64Encoded: false
};

callback(null, response);

But I get the following error in my frontend Angular application.

Access to XMLHttpRequest at 'https://xxxxxxxxx.execute-api.us-east-1.amazonaws.com/dev/price' from origin 'http://127.0.0.1:8080' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status.

You are being blocked at the API level. Not your lambda. You may want to add that configuration. — Darren Forsythe

David Liao David Liao · Accepted Answer · 2020-04-14T02:38:01

If you are using API Gateway HTTP APIs (not sure if this is relevant for the REST APIs):

Lets say I have an endpoint at /POST products. I had to add another endpoint at /OPTIONS products and integrate it with a simple Lambda function that just returns the HTTP 200 OK (or HTTP 204 No Content), and the "Access-Control-Allow-Origin": "*" header (or even better, specify the URL of your origin/client).

This is because browsers issue a preflight /OPTIONS request to the same endpoint, before issuing the actual request (see more), for all HTTP requests except GET and POST with certain MIME types (source).

Can't access API with Lambda and API Gateway

2 Answers