docker-compose NodeJS + Mongodb with mongoose, dynamically get the mongo container ip

I have a dockerized nodejs app linked with a mongo container. Here is the dockerfile and docker-compose.yml :

FROM node:boron

# Create app directory
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

# Install app dependencies
COPY package.json /usr/src/app/
RUN npm install

# Bundle app source
COPY . /usr/src/app

EXPOSE 3000
CMD [ "npm", "start" ]

---

version: "2"
services:
  web:
    build: .
    volumes:
      - .:/usr/src/app
    ports:
      - "3000:3000"
    links:
      - mongo
  mongo:
    image: mongo
    ports:
        - "27017:27017"

and here is my app.js handling the mongo connection via the mongoose tool :

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');


var index = require('./routes/index');
var users = require('./routes/users');

var app = express();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');

//DB setup
mongoose.connect('mongodb://172.19.0.2/test');

// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', index);
app.use('/users', users);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
});

module.exports = app;

My app launches, if I go on http://localhost:3000 on my computer my view displays and in my terminal I see that mongo accepted a connection.

---

Problem is :

In my app.js I added manually the mongo container ip. I believe if I push this app on github and someone gets it. His mongo container ip won't be the same as the one i added manually. Is there some way to dynamise all of this so that my app gets automatically the mongo container ip?

via Aria Groult