Node: wait till function is finished before executing process.exit

Question

I'm very new to node. I've written a script which does a telnet. If the telnet works we do a traceroute and exit properly (this works). When the telnet doesn't work I still do a traceroute and try to exit with exit status -1. This does not work. The traceroute is not shown and the process.exit(1) appears too early/does not wait till the output of the traceroute.

This is my script (it's a lambda):

'use strict';
const Traceroute = require('nodejs-traceroute');
const isPortReachable = require('is-port-reachable');

console.log('Loading function');
process.env.PATH = `${process.env.PATH}:${process.env.LAMBDA_TASK_ROOT}/bin`;


async function doTraceroute() {
    try {
        const tracer = new Traceroute();
        tracer
            .on('pid', (pid) => {
                console.log(`pid: ${pid}`);
            })
            .on('destination', (destination) => {
                console.log(`destination: ${destination}`);
            })
            .on('hop', (hop) => {
                console.log(`hop: ${JSON.stringify(hop)}`);
            })
            .on('close', (code) => {
                console.log(`close: code ${code}`);
            });
    
        tracer.trace('100.216.125.9');
    } catch (ex) {
        console.log(ex);
    }
}

exports.handler = (event, context, callback) => {
    (async () => {
        console.log('Is port 9092 reachable of MC Kafka host? True or False')
        let output = await isPortReachable(9092, {host: '100.216.125.9'})
        if (output) {
            console.log('Telnet worked: do traceroute')
            await doTraceroute();
        } else {
            console.log('Telnet failed: do traceroute')
            await doTraceroute();
            console.log("Exit with error")
            process.exit(1)
        }
    })();
};

How can I solve it? The current output when the telnet failed is:

START RequestId: 315b0ac5-09d7-4b72-8ff7-746b28241f79 Version: $LATEST
2020-11-09T07:25:07.841Z    315b0ac5-09d7-4b72-8ff7-746b28241f79    INFO    Is port 9092 reachable of MC Kafka host? True or False
2020-11-09T07:25:08.851Z    315b0ac5-09d7-4b72-8ff7-746b28241f79    INFO    Telnet failed: do traceroute
2020-11-09T07:25:08.909Z    315b0ac5-09d7-4b72-8ff7-746b28241f79    INFO    pid: 20
2020-11-09T07:25:08.910Z    315b0ac5-09d7-4b72-8ff7-746b28241f79    INFO    Exit with error
END RequestId: 315b0ac5-09d7-4b72-8ff7-746b28241f79
REPORT RequestId: 315b0ac5-09d7-4b72-8ff7-746b28241f79  Duration: 1150.28 ms    Billed Duration: 1200 ms    Memory Size: 128 MB Max Memory Used: 70 MB  Init Duration: 176.80 ms    
RequestId: 315b0ac5-09d7-4b72-8ff7-746b28241f79 Error: Runtime exited with error: exit status 1
Runtime.ExitError

without showing the traceroute. The traceroute is shown when the telnet succeeds and there is no exit 1.

Answer 1

You can wrap the traceroute processing in a promise and await this promise:

function doTraceroute() {
    return new Promise((resolve, reject) => {
        try {
            const tracer = new Traceroute();
            tracer
                .on('pid', (pid) => {
                    console.log(`pid: ${pid}`);
                })
                .on('destination', (destination) => {
                    console.log(`destination: ${destination}`);
                })
                .on('hop', (hop) => {
                    console.log(`hop: ${JSON.stringify(hop)}`);
                })
                .on('close', (code) => {
                    console.log(`close: code ${code}`);
                    resolve();
                });

            tracer.trace('100.216.125.9');
        } catch (ex) {
            console.log(ex);
            reject(ex);
        }
    });
}

You can then await the returned promise:

await doTraceroute();