How to get docker mapped ports from node.js application?

Question

I would like to get mapped port from inside node.js application.

ex.

docker-compose:

my-app:
    build:
        context: ./my-app
           


        

Answer 1

What about using shelljs?

const shelljs = require('shelljs');

const output = shelljs.exec('docker ps --format {{.Ports}}', {silent: true}).stdout.trim();

console.log(output); // 80/tcp
                     // 19999/tcp
                     // 9000/tcp
                     // 8080/tcp, 50000/tcp

The output is a string, now let's map the response.

const shelljs = require('shelljs');

const output = shelljs.exec('docker ps --format {{.Ports}}', {silent: true}).stdout.trim();

const ports = output.split('\n').map(portList => portList.split(',').map(port => Number(port.split('/')[0].trim())));

This way ports return an array of arrays containing the ports:

[ [ 80 ], [ 19999 ], [ 9000 ], [ 8080, 50000 ] ]

In your case, you want the number between : and ->. So you can do this:

const shelljs = require('shelljs');

const output = shelljs
  .exec('docker ps --format {{.Ports}}', { silent: true })
  .stdout.trim();

const aoa = output.split('\n').map(portList => portList.split(','));

console.log(aoa); // [ [ '9000/tcp', ' 0.0.0.0:9000->123/tcp ' ], [ ' 80/tcp' ] ]

let ports = [];

aoa.forEach(arr => {
  arr.forEach(p => {
    // match strings which contains :PORT-> pattern;
    const match = p.match(/:(\d+)->/);
    if (match) {
      ports.push(Number(match[1]));
    }
  });
});

console.log(ports); // [ 9000 ]

Finally, you need to install docker inside your container and connect docker socks as explained here.

Update 29/06/2019:

As said by @Tarun Lalwani, if sharing docker socks is a problem, you may create an app which shares the network with your main app and has a GET method that returns ports.