AWS API Gateway error response generates 502 "Bad Gateway"

Question

I have an API Gateway with a LAMBDA_PROXY Integration Request Type. Upon calling context.succeed in the Lambda, the response header is sent back with code 302 as expected (shown below). However, I want to handle 500 and 404 errors, and the only thing I am sure about so far, is that I am returning the error incorrectly as I am getting 502 Bad Gateway. What is wrong with my context.fail?

Here is my handler.js

const handler = (event, context) => { 
    //event consists of hard coded values right now
    getUrl(event.queryStringParameters)
    .then((result) => {
        const parsed = JSON.parse(result);
        let url;
        //handle error message returned in response
        if (parsed.error) {
            let error = {
                statusCode: 404,
                body: new Error(parsed.error)
            }
            return context.fail(error);
        } else {
            url = parsed.source || parsed.picture;
            return context.succeed({
                statusCode: 302,
                headers: {
                  Location : url
                }
              });
        }
    });
};

Answer 1

If you throw an exception within the Lambda function (or context.fail), API Gateway reads it as if something had gone wrong with your backend and returns 502. If this is a runtime exception you expect and want to return a 500/404, use the context.succeed method with the status code you want and message:

if (parsed.error) {
  let error = {
    statusCode: 404,
    headers: { "Content-Type": "text/plain" } // not sure here
    body: new Error(parsed.error)
}
return context.succeed(error);