How to troubleshoot this AWS lambda error - An error has occurred: Received error response from Lambda: Unhandled?

Question

I'm new to AWS. I'm build chatbot using aws lex and aws lambda c#. I'm using sample aws lambda C# program

namespace AWSLambda4
{
    public class Function
    {

        /// <summary>
        /// A simple function that takes a string and does a ToUpper
        /// </summary>
        /// <param name="input"></param>
        /// <param name="context"></param>
        /// <returns></returns>
        public string FunctionHandler(string input, ILambdaContext context)
        {
            try
            {
                return input?.ToUpper();
            }
            catch (Exception e)
            {

                return "sorry i could not process your request due to " + e.Message;
            }
        }
    }
}

I created a slot in aws lex to map first parameter input . But i'm always getting this error An error has occurred: Received error response from Lambda: Unhandled

In Chrome network tab i could see Error- 424 Failed Dependency which is related to authentication.

Please help how to troubleshoot AWS lambda C# error which is used by aws lex. I came across cloudwatch but I'm not sure about that.

Thanks!

Solution 1

Here is what worked for me:

Lex sends request in LexEvent Class type and expects response in LexResponse Class type.So i changed my parameter from string to LexEvent and return type from string to LexResponse.

public LexResponse FunctionHandler(LexEvent lexEvent, ILambdaContext context)
    {
        //Your logic goes here.
        IIntentProcessor process;

        switch (lexEvent.CurrentIntent.Name)
        {
            case "BookHotel":
                process = new BookHotelIntentProcessor();
                break;
            case "BookCar":
                process = new BookCarIntentProcessor();
                break;                
            case "Greetings":
                process = new GreetingIntentProcessor();
                break;
            case "Help":
                process = new HelpIntentProcessor();
                break;
            default:
                throw new Exception($"Intent with name {lexEvent.CurrentIntent.Name} not supported");
        }


        return process.Process(lexEvent, context);// This is my custom logic to return LexResponse
    }

But i'm not sure about the root cause of the issue.

Solution 2

The communication between Lex and Lambda is not straight forward like normal functions. Amazon Lex expects output from Lambda in a particular JSON format and data like slot details etc are also sent to Lambda in a similar JSON. You can find the blueprints for them here: Lambda Function Input Event and Response Format. Make sure your C# code also return a JSON in the similar fashion, so that Lex can understand and do the further processing.

Hope it helps!

Comments

[ManirajSS]

Lambda have both handled and un-handled error.Since it is unhandled error the lambda method itself not invoked i guess.And lex console states Error- 424 Failed Dependency which is related to authentication.So i think its more related to configuration related error rather than coding related error.

[yashhy]

@ManirajSS I have an error which says Received invalid response from Lambda and in network tab it seems to be a 424. do you know the possible route cause?

[ManirajSS]

@yashhy i have resolved my issue. Please see my answer and let me know if you have any doubts.

[yashhy]

as @Repakula mentioned the 424 error response seems to be a Lex return type issue? and in my case im using nodejs and following the sample structure like stated here

[yashhy]

I solved the problem as suggested by @ Repakula see the detailed answer here