Passing custom errors back to AWS API Gateway from AWS Lambda using node.js

Question

I'd really like to be able to pass custom errors back out of my Lambda function via the API Gateway.

I'm generating the errors this way:

if (error) { // failure

        APIGatewayResult = { // set error object
            statusCode: 608,
            message: 'File upload to buffer failed.',
            error: error
        };
        done();

    };

I'm fairly certain the format above is either parsed incorrectly or I can't pass it back out like this:

done = (err, res) => callback(null, {
        statusCode: err ? APIGatewayResult.statusCode : APIGatewayResult.statusCode,
        body: err ? JSON.stringify(APIGatewayResult) : JSON.stringify(APIGatewayResult),
        headers: {
            'Content-Type': 'application/json',
        },
});

I'd like the response I get from API gateway to look like this:

{
    "statusCode": 608,
    "message": "File upload to buffer failed.",
    "error": {}
}

Instead of this:

{
    "message": "Internal server error"
}

Internal server error occurs for unhandled errors inside lambda, you can look at the cloudwatch logs to find out the error. — Jishnu
– Jishnu, Commented Jul 16, 2021 at 4:33
@Jishnu - the point is to create an API that I can sell to others. They will not have access to cloudwatch, but they will have access to the response from the API Gateway. — Sully1570
– Sully1570, Commented Jul 16, 2021 at 6:14

j-petty · Accepted Answer · 2021-07-16 05:25:07Z

1

There are two parts to your question:

1) How to handle Lambda error messages in API Gateway:

There are numerous guides available which explain how to parse Lambda error responses in API Gateway to return them in the desired format to consumers. For example: Error Handling Patterns in Amazon API Gateway and AWS Lambda.

Important to note that you're parsing null to the first parameter of the callback function from your lambda. The first parameter is the error response message, so by providing it as null the Lambda will be returning a successful 200 response back to API Gateway.

2) How to override the generic unhandled exception message in API Gateway:

This is required because as mentioned in the comments, the error you're receiving appears to have been thrown due to an unhandled exception in your application. You'll need to review the logs to identify the source of the issue.

But to change the format of the default error response object you'll need to add a custom Gateway response in API Gateway.

It's difficult to offer a more concrete example given the limited information provided but this should be enough to point you in the right direction to find what you're looking for.

answered Jul 16, 2021 at 5:25

j-petty

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1 Comment

Sully1570 Over a year ago

Thank you! Would still be beating my head against the keys w/o your help.

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