AWS lambda api gateway error “Malformed Lambda pro

Question

I am trying to set up a hello world example with AWS lambda and serving it through api gateway. I clicked the "Create a Lambda Function", which set up the api gatway and selected the Blank Function option. I added the lambda function found on AWS gateway getting started guide:

exports.handler = function(event, context, callback) {
  callback(null, {"Hello":"World"});  // SUCCESS with message
};

The issue is that when I make a GET request to it, it's returning back a 502 response { "message": "Internal server error" }. And the logs say "Execution failed due to configuration error: Malformed Lambda proxy response".

Answer 1

If lambda is used as a proxy then the response format should be

{
"isBase64Encoded": true|false,
"statusCode": httpStatusCode,
"headers": { "headerName": "headerValue", ... },
"body": "..."
}

Note : The body should be stringified

Answer 2

For anyone else who struggles when the response appears valid. This does not work:

callback(null,JSON.stringify( {
  isBase64Encoded: false,
  statusCode: 200,
  headers: { 'headerName': 'headerValue' },
  body: 'hello world'
})

but this does:

callback(null,JSON.stringify( {
  'isBase64Encoded': false,
  'statusCode': 200,
  'headers': { 'headerName': 'headerValue' },
  'body': 'hello world'
})

Also, it appears that no extra keys are allowed to be present on the response object.

Answer 3

If you're using Go with https://github.com/aws/aws-lambda-go, you have to use events.APIGatewayProxyResponse.

func hello(ctx context.Context, event ImageEditorEvent) (events.APIGatewayProxyResponse, error) {
    return events.APIGatewayProxyResponse{
        IsBase64Encoded: false,
        StatusCode:      200,
        Headers:         headers,
        Body:            body,
    }, nil
}

Answer 4

In case the above doesn't work for anyone, I ran into this error despite setting the response variable correctly.

I was making a call to an RDS database in my function. It turned out that what was causing the problem was the security group rules (inbound) on that database.

You'll probably want to restrict the IP addresses that can access the API, but if you want to get it working quick / dirty to test out if that change fixes it you can set it to accept all like so (you can also set the range on the ports to accept all ports too, but I didn't do that in this example):

Answer 5

I've tried all of above suggestion but it doesn't work while body value is not String

return {
    statusCode: 200,
    headers: {
        "Content-Type": "application/json",
        "Access-Control-Allow-Origin": "*"
    },
    body: JSON.stringify({
        success: true
    }),
    isBase64Encoded: false
};

Answer 6

Usually, when you see Malformed Lambda proxy response, it means your response from your Lambda function doesn't match the format API Gateway is expecting, like this

{
    "isBase64Encoded": true|false,
    "statusCode": httpStatusCode,
    "headers": { "headerName": "headerValue", ... },
    "body": "..."
}

If you are not using Lambda proxy integration, you can login to API Gateway console and uncheck the Lambda proxy integration checkbox.

Also, if you are seeing intermittent Malformed Lambda proxy response, it might mean the request to your Lambda function has been throttled by Lambda, and you need to request a concurrent execution limit increase on the Lambda function.