CODEWITHSUNDEEP
node.jsamazon-web-servicesasynchronousaws-lambda
user2127726
user2127726

Reputation: 145

Return data from async AWS Lambda

How do I get the data back from a lambda invoked with as an event to the calling function?

Essentially the lambda function I have is:

exports.handler = function(event, context, callback) {
    var data = {};
    data.foo ='hello';
    callback(null, data)
}

and the invoking function looks like this:

var AWS = require('aws-sdk');

var lambda = new AWS.Lambda();
var params = {
    FunctionName: 'SomeFunction',
    InvocationType: 'Event'
};

lambda.invoke(params, function (err, data) {
    if (err) {
        console.log(err, err.stack); // an error occurred
    } else {
        console.log(JSON.stringify(data, null, 2));
    }
});

However the only thing I get back from the function is

{
  "StatusCode": 202,
  "Payload": ""
}

I thought the point of the callback parameter was to allow the invoking function to get the data when the function has finished. Am I using it wrong or is what I am asking not possible with Lambdas?

Upvotes: 1

Views: 3599

Answers (2)

f.cipriani
f.cipriani

Reputation: 3527

As @MatthewPope commented in this answer, if you do need the results from an asynchronous Lambda execution, you should consider having the Lambda function write its results to S3 (or something to that effect) at a known location where clients of the Lambda function can periodically check for the existence of the result.

Upvotes: 0

idbehold
idbehold

Reputation: 17168

When you invoke the Lambda function you need to set the InvocationType to 'RequestResponse' instead of 'Event'.

When using the Event type your callback is invoked when the payload has been received by AWS's servers. When using the RequestResponse type your callback is invoked only after the Lambda function has completed and you will receive the data it provided to its callback. It is not possible to do what you want with the Event type.

Upvotes: 9

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