Lambda Function does not return until async request ends

Question

I want to make a function that calls an API (third party) and returns immediately, but it is waiting for API response.

Here is the code sample:

var request = require('request');

// When I call functionOne it should trigger functionTwo and should end immediately, 
// but unfortunately, it is waiting for functionTwo to end
module.exports.functionOne = (event, context, cb) => {
    const uri = 'https://xxxxxxxxx.execute-api.us-east-1.amazonaws.com/dev/functionTwo';
    request.post({ uri: uri });
    cb(null, "done functionOne");
};

module.exports.functionTwo = (event, context, cb) => {
    console.log("i'm functionTwo");
    setTimeout(function () {
        console.log("I'm functionTwo about to end");
        context.succeed("done functionTwo");
    }, 5000);
};

Moreover, if i try to call context.succeed() instead of cb(), it even prevent API call and function return immediately without calling the API.

I have also created an issue on GitHub.

Additional info:

Serverless Framework: v1.0.0-rc.2
Node: v6.9.1
OS: Win 10

Zanon · Accepted Answer · 2016-11-20 18:48:45Z

3

Sorry, but you can't achieve what you want, at least not in this way.

When you call another function using request.post(), you must provide a callback and you must wait for it to finish.

What you could do is to call request.abort(), but this is a hacky solution.

module.exports.functionOne = (event, context, cb) => {
    const uri = 'https://xxxxxxxxx.execute-api.us-east-1.amazonaws.com/dev/functionTwo';
    const r = request.post({ uri: uri }, (error, response, body) => {
        cb(error, "done functionOne");
    });

    r.abort();
    cb(null, 'forced abort on functionOne');
};

Why is this hacky? Because you can't abort immediately. You need to wait a few milliseconds for the request to be received in the other server, but there is no way to know exactly when it happens.

If you know that the second Lambda will run for 2 minutes, you could add a setTimeout function to abort the request after 5 seconds and avoid having the functionOne running for a long time in a idle state. But again, this is a bad solution.

Why don't you place the functionTwo code inside functionOne to avoid starting a second Lambda?

Another workaround would be to call a SNS topic from functionOne and configure this topic to trigger functionTwo.

answered Nov 20, 2016 at 18:48

Zanon

31k21 gold badges119 silver badges127 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Inzamam Malik Over a year ago

FunctionTwo is here just for example, in actual case there is an api which is third party, and i'm sending post request to that api with some data, and actually it is slack api

Zanon Over a year ago

Ok, so I suggest that you create another question specific to the Slack API. If it was another Lambda function, you could use SNS because it returns in just a few milliseconds. If Slack takes several seconds to complete, I don't know if they provide another way to queue the request without needing to wait.

Zanon Over a year ago

Otherwise, you can abort the request to force Lambda to stop early, but as I said, you need to wait a few moments before Slack receives the request.

Inzamam Malik Over a year ago

aborting request does not solved my problem unfortunately

shobhit agarwal · Accepted Answer · 2021-07-23 10:56:53Z

0

In your handler you can use flag callbackWaitsForEmptyEventLoop = false

    module.exports.functionOne = (event, context, cb) => {
    context.callbackWaitsForEmptyEventLoop = false
    const uri = 'https://xxxxxxxxx.execute-api.us-east-1.amazonaws.com/dev/functionTwo';
    request.post({ uri: uri });
    cb(null, "done functionOne");
    };

answered Jul 23, 2021 at 10:56

shobhit agarwal

832 silver badges4 bronze badges

Collectives™ on Stack Overflow

Lambda Function does not return until async request ends

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related