Setup

Requirements

Before you go through this fun tutorial ensure:

You at least have an understanding of javascript and terminal commands.
You should know what Docker is and in theory how it works.
You have should node and npm installed on your computer. You can do this by typing this in your terminal.

$ node --version && node --version

Also, since we talking containers well you need docker installed.

$ docker --version

Create a new project

Create our project folder, where our codebase will be housed

$ mkdir docker_nodejs_app

Let's change the directory to our app folder.

$ cd docker_nodejs_app

Since this is a node project, we need a package.json file to track our project dependencies.

To create one pretty fast type this in your terminal.

$ npm init -y

We will be using express as our default node web framework.

$ npm install express --save # Introduce the save flag to track it in the package.json file

{
  "name": "docker_node_app",
  "version": "1.0.0",
  "description": "nodejs image demo",
  "author": "your name",
  "license": "MIT",
  "main": "app.js",
  "keywords": [],
  "scripts": {
      "start":"node app.js"
  },
  "dependencies": {
    "express": "^4.16.4"
  }
}

Create and run our server

We will create a simple express server. Let's create the file that will hold our server code.

You can use the terminal to create the file

$ touch app.js # Creates the file from the terminal

Or your locally installed code editor.

Let us write our server code.

"use strict"; // Ensures our code is compiled in strict mode

// Lets import our web framework
var express = require("express");

// Initialise our app
const app = express();

// Lets set our port
/**
 * The default port number is `3000`
 * Take note on that as we will come to that.
 */
app.set("port", 3000);

/**
 * To ensure works as it should we will create a
 * simple endpoint to return a json response
 */

// Define our json response
const data = {
  blog_name: "docker_nodejs_app",
  blog_author: "wachira (tesh254)",
  blog_author_twitter: "@wachira_dev"
};

// Define out GET request endpoint
app.get("/", (req, res) => {
  res.status(200).json(data);
});

// Initialize our server
app.listen(app.get("port"), () => {
  console.log(`Server listening on port ${app.get("port")}`);
});

Let's run it, it's a simple server meaning its bug-free.

$ node app.js

You should see the same text on your terminal.

Let's test our endpoint on our browser.

Finally what the blog is about.....DOCKER

For you to run your server within a container you a couple of things:

Dockerfile: defines what goes on in the environment inside your container.
docker-compose.yml: Not a must but comes in handy if you plan to add services like a database
Dependency file: Contains the packages needed to run your application successfully e.g. package.json file for node or requirements.txt for python.
.dockerignore: Not a must but it allows you to exclude files from the context like a .gitignore file allows you to exclude files from your git repository.

Let's create and write our Dockerfile

$ touch Dockerfile

You can copy and paste the configurations to your Dockerfile.

# Define the image we will use and version
# latest just means we need the latest nodejs image available
FROM node:8

# Create an app directory to hold the application code
WORKDIR /usr/docker_nodejs_app/src/app

# Duplicate the dependency file to the container's project root directory.
COPY package*.json ./

# Install app dependencies
RUN npm install

# Bundle app source inside the docker image
COPY . .

# Expose our app port inside the app and 
EXPOSE 3000:3000

# Define commands that will run the app
CMD ["npm", "start"]