Api Gateway: AWS Subdomain for Lambda Integration

Question

I'm attempting to integrate my lambda function, which must run async because it takes too long, with API gateway. I believe I must, instead of choosing the "Lambda" integration type, choose "AWS Service" and specify Lambda. (e.g. this and this seem to imply that.)

However, I get the message "AWS ARN for integration must contain path or action" when I attempt to set the AWS Subdomain to the ARN of my Lambda function. If I set the subdomain to just the name of my Lambda function, when attempting to deploy I get "AWS ARN for integration contains invalid path".

What is the proper AWS Subdomain for this type of integration?

Note that I could also take the advice of this post and set up a Kinesis stream, but that seems excessive for my simple use case. If that's the proper way to resolve my problem, happy to try that.

Edit: Included screen shot

Edit: Please see comment below for an incomplete resolution.

Answer 1

So it's pretty annoying to set up, but here are two ways:

1. Set up a regular Lambda integration and then add the InvocationType header described here http://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html. The value should be 'Event'.

   • This is annoying because the console won't let you add headers when you have a Lambda function as the Integration type. You'll have to use the SDK or the CLI, or use Swagger where you can add the header easily.

2. Set the whole thing up as an AWS integration in the console (this is what you're doing in the question), just so you can set the InvocationType header in the console

   • Leave subdomain blank
   • "Use path override" and set it to /2015-03-31/functions/<FunctionARN>/invocations where <FunctionARN> is the full ARN of your lambda function
   • HTTP method is POST
   • Add a static header X-Amz-Invocation-Type with value 'Event'

http://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html

Answer 2

The other option, which I did, was to still use the Lambda configuration and use two lambdas. The first (code below) runs in under a second and returns immediately. But, what it really does is fire off a second lambda (your primary one) that can be long running (up to the 15 minute limit) as an Event. I found this more straightforward.

/**
 * Note: Step Functions, which are called out in many answers online, do NOT actually work in this case.  The reason
 * being that if you use Sequential or even Parallel steps they both require everything to complete before a response
 * is sent.  That means that this one will execute quickly but Step Functions will still wait on the other one to
 * complete, thus defeating the purpose.
 *
 * @param {Object} event The Event from Lambda
 */
exports.handler = async (event) => {
    let params = {
      FunctionName: "<YOUR FUNCTION NAME OR ARN>",
      InvocationType: "Event",  // <--- This is KEY as it tells Lambda to start execution but immediately return / not wait.
      Payload: JSON.stringify( event )
    };

    // we have to wait for it to at least be submitted. Otherwise Lambda runs too fast and will return before
    // the Lambda can be submitted to the backend queue for execution
    await new Promise((resolve, reject) => {
        Lambda.invoke(params, function(err, data) {
            if (err) {
                reject(err, err.stack);
            }
            else {
                resolve('Lambda invoked: '+data) ;
            }
        });
    });

    // Always return 200 not matter what
    return {
        statusCode : 200,
        body: "Event Handled"
    };

};