Returning custom http status codes on AWS Lambda error - aws-lambda

Question

I'm working with an AWS Lambda with serverless framework and I want to return a custom http status code when an error occurs but I'm always getting a 502 status code when I call my endpoint with axios.
module.exports.handler = async (event, context, callback) => {
try {
// some stuff
} catch (err) {
// error here
let myErrorObj = {
errorType : "InternalServerError",
httpStatus : 500,
requestId : context.awsRequestId,
trace : {
"function": "abc()",
"line": 123,
"file": "abc.js"
},
body: err
}
callback(JSON.stringify(myErrorObj));
}
}
But the object I'm getting back contains the property status: 502 and data.message: "Internal server error"
Any ideas of what is going on here?

Answer 1

status code 502 indicates the lambda's response to API Gateway is in an incorrect format.
The correct response for an async function (if not integration method stated in serverless YAML file, it would use Lambda Proxy Integration):
export const dummyFunction = async (event, context, callback) =>
{
// ... logic
return {
statusCode: 500,
body: JSON.stringify({...data}),
}
};
Callback is only for non-async function only. Please refer to full documentation.

Answer 2

Are you using API Gateway with your Lambda? If so, what you are returning in the callback is incorrect. The object you return must match this format: https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-proxy-integrations.html#api-gateway-simple-proxy-for-lambda-output-format
So you can either just callback(err) and let AWS generate a 500 or if you want the added error context something like:
let myErrorObj = {
statusCode : 500,
body: JSON.stringify({
requestId : context.awsRequestId,
trace : {
"function": "abc()",
"line": 123,
"file": "abc.js"
}
error: err
}
})
}
callback(null, myErrorObj);
If you want requestId and trace attributes you would need to add them into the body.