AWS Lambda function to check whether the site is available - node.js

Question

I want to create an AWS Lambda function to check whether the site is available. I tried this function.
'use strict';
var url = require('url');
var target = 'https://www.google.com'; // Change this one
exports.handler = function(event, context, callback) {
var urlObject = url.parse(target);
var mod = require(
urlObject.protocol.substring(0, urlObject.protocol.length - 1)
);
console.log('[INFO] - Checking ' + target);
var req = mod.request(urlObject, function(res) {
res.setEncoding('utf8');
res.on('data', function(chunk) {
console.log('[INFO] - Read body chunk');
});
res.on('end', function() {
console.log('[INFO] - Response end');
callback();
});
});
req.on('error', function(e) {
console.log('[ERROR] - ' + e.message);
callback(e);
});
req.end();
};
I tried this in "How it works" section before create the actual function. But when I run this, I get an error "Process exited before completing request"
My objective is to send an alert if the site is down (using AWS cloud-watch).

Answer 1

Your code terminates because you're invoking req.end before any the events are invoked. Under the hood, these APIs use the EventEmitter API in NodeJS so it publishes events to the channels that are listening to them, but since all of this happens asynchronously, req.end is being invoked before any of these events are fired.
You can greatly simplify your code by using the request module. Just pack it with your dependencies.
I have refactored your code a little bit to use async/await as well, so I needed to promifisy the callback. It's a good practice to do so. If you want to send a notification when something goes wrong, just put the code inside the catch block.
'use strict';
const target = 'https://www.google.com'; // Change this one
const request = require('request')
const handler = async (event) => {
try {
const data = await new Promise((res, rej) => {
request.get(target, (err, data) => {
if (err) {
return rej(err)
}
return res(data)
})
})
console.log(data)
} catch (e) {
console.log(e)
//send notification
}
};