AWS lambda exits before callback hit

Question

I am experiencing an issue with AWS Lambda with Node 8.10 existing early with the implicit null returned callback:

const request = require('request');

exports.handler = async (event, ctx, callback) => {
    console.log(`Fetching '${event.url}'...`);
    request(event.url, (err, body) => {
        if (err) return callback(err);
        return callback(null, body);
    });
}

This is a basic example of the problem I have in my own much larger lambda function. Essentially, when I make a call to a 3rd party resource, the Lambda finishes before the callback is reached.

I have read several documentation pages and SO posts that refer to: callbackWaitsForEmptyEventLoop but setting this to false does not change the behaviour.

I have managed to force it to wait for the response by wrapping the code in a promise then using await before calling callback but is this really necessary?

exports.handler = async (event, ctx, callback) => {
    
    const executeLambda = new Promise((resolve, reject) => {
        console.log(`Fetching '${event.url}'...`);
        request(event.url, (err, body) => {
            if (err) return reject(err);
            return resolve(body);
        });
    });

    await executeLambda
        .then((res) => callback(null, res))
        .catch(callback);
}

Note: I am mocking this locally with docker run --rm -v "$PWD":/var/task lambci/lambda:nodejs8.10 index.handler '{"url": "https://www.google.com"}'

phobos · Accepted Answer · 2018-06-20 12:41:09Z

2

The problem was that I declared the handler with async. The following works:

const request = require('request');

exports.handler = (event, ctx, callback) => {
    console.log(`Fetching '${event.url}'...`);
    request(event.url, (err, body) => {
        if (err) return callback(err);
        return callback(null, body);
    });
}

answered Jun 20, 2018 at 12:41

phobos

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