HOW TO DEBUG NODE.JS APP IN A DOCKER CONTAINER

Dockerizing a Node.js web app: This example is to show you how to get a Node.js application into a Docker container. This is for development, and not for production deployment. it also assumes you have a working Docker installation and a basic understanding of how a Node.js application is structured.

In the first part of this example, we will create a simple web application in Node.js, then we will build a Docker image for that application, and lastly we will run the image as a container.

Docker allows you to package an application with all of its dependencies into a standardized unit, called a container, for software development. A container is a stripped-to-basics version of a Linux operating system. An image is a software you load into a container.

Create the Node.js app

First, create a new directory where all the files would live. In this directory create a package.json file that describes your app and its dependencies:

######{"name": "docker_nodeJs-web_app","version": "1.0.0","description": "Node.js on Docker","author": "Gaurav Srivsatva <first.last@example.com>","main": "server.js","scripts": {"start": "node server.js"},"dependencies": {"express": "^4.13.3"}}######

Then, create a server.js file that defines a web app using the Express.js framework:

######
'use strict';
const express = require('express');
// Constants
const PORT = 8080;
// App
const app = express();
app.get('/', function (req, res) {
res.send('Hello Linux-ponit\n');
});
app.listen(PORT);
console.log('Running on http://localhost:' + PORT);######

In the next steps, we’ll look at how you can run this app inside a Docker container using the official Docker image. First, you’ll need to build a Docker image of your app.

Creating a Dockerfile

The first thing we need to do is define from what image we want to build from. Here we will use the latest LTS (long term support) version boron of node available from the Docker Hub:

vim Dockerfile
FROM node:latest

Next we create a directory to hold the application code inside the image, this will be the working directory for your application:

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

This image comes with Node.js and NPM already installed so the next thing we need to do is to install your app dependencies using the npm binary:

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

To bundle your app’s source code inside the Docker image, use the COPY instruction:

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

Your app binds to port 8080 so you’ll use the EXPOSE instruction to have it mapped by the docker daemon:

EXPOSE 8080

Last but not least, define the command to run your app using CMD which defines your runtime. Here we will use the basic npm start which will run node server.js to start your server:

CMD [ "npm", "start" ]

Now your Dockerfile should look like this:

FROM node:latest# Create app directoryRUN mkdir -p /usr/src/app
WORKDIR /usr/src/app# Install app dependenciesCOPY package.json /usr/src/app/
RUN npm install# Bundle app sourceCOPY . /usr/src/app
EXPOSE 8080
CMD [ "npm", "start" ]

Create a .dockerignore file in the same directory as your Dockerfile with following content:

• node_modules
• npm-debug.log

This will prevent your local modules and debug logs from being copied onto your Docker image and possibly overwriting modules installed within your image.