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Introduction to Docker

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Configuring the App

4:05 with Jay McGavren and Jared Smith

In this final stage, we'll take everything we've learned so far and Dockerize a simple Node.js web app.

This Node.js web app simply listens for connections on port 80, and responds with the message "Hello from Node.js!".

server.js

'use strict';

const express = require('express');

// Constants
const PORT = 80;
const HOST = '0.0.0.0';

// App
const app = express();
app.get('/', (req, res) => {
  res.send('Hello from Node.js!\n');
});

app.listen(PORT, HOST);
console.log(`Running on http://${HOST}:${PORT}`);

Like most Node apps, this app also includes a file named package.json that defines how it's built. The "start" line is particularly important; it contains the command that will run the server.

package.json

{
  "name": "docker_web_app",
  "version": "1.0.0",
  "description": "Node.js on Docker",
  "author": "Jared Smith <jared@jaredthecoder.com>",
  "main": "server.js",
  "scripts": {
    "start": "node server.js"
  },
  "dependencies": {
    "express": "^4.13.3"
  }
}

Now that we have our server code, it's time to build the Dockerfile to deploy it!

# Build off this base image
FROM node:7

# Set up app directory
WORKDIR /usr/src/app

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

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

# Expose the server to the host machine
EXPOSE 8080

# Run this command on startup
ENTRYPOINT ["npm", "start"]

New Terms

  • Node.js: A JavaScript runtime for non-browser environments.
  • package.json: A file that defines a JavaScript packages settings (i.e. how to build it, how to start it, metadata, etc.)
  • Express: A JavaScript/Node.js web server framework, like Flask or Django for Python, or Sinatra or Ruby on Rails for Ruby.
  • NPM: Node.js Package Manager, the package manager for installing JavaScript/Node.js packages into your development or production environment.

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    In this final stage, we'll take everything we've learned so far and 0:00
    dockerize this simple Node.js web app. 0:04
    See the teacher's notes if you'd like to retrieve a copy of the app for yourself. 0:06
    Node.js is a run-time that allows you to run JavaScript on a server. 0:10
    This app simply listens for connections on port 80, and 0:15
    responds with the message, Hello from Node.js. 0:18
    It's quite short, 0:21
    because it relies on the express framework to handle browser requests. 0:23
    So to make this work in a Docker container, 0:27
    we're going to need both Node.js and the express library installed. 0:29
    Like most node apps, this app also includes a file named package.json, 0:33
    that defines how it's built. 0:38
    The start line is particularly important. 0:40
    It contains the command that will run the server. 0:42
    Now that we have our server code, 0:46
    it's time to build the Docker file to deploy it. 0:47
    As usual, in the same directory as the app code, create a file, 0:50
    named, Docker file, with a capital D, and no file name extension. 0:54
    The first thing we'll want to do is ensure our new docker image is 0:58
    using an appropriate base image, we'll do that using the from instruction. 1:02
    From takes the name and tag of an image to use, 1:07
    we'll use the Node image from docker hub. 1:10
    The maintainers of the node docker images chose to tag their images with the node 1:13
    version number so we'll write a colon and then a tag with the version we want, 7. 1:18
    Now we want to create a directory inside image that will house our app. 1:23
    The WORKDIR instruction will create a directory, and also ensure that all 1:27
    remaining instructions in this Docker file, operate within that directory. 1:32
    We'll give it a path of /usr/src/app. 1:37
    Next we need to install our app's dependencies. 1:41
    Since we're using the node base image, Node.js and 1:44
    its package manager, NPM will already be installed. 1:49
    We can just use NPM to install the express library and any other dependencies for us, 1:54
    but NPM needs our package.json file so that it knows what packages to install. 2:01
    So we'll use the copy instruction to copy the package.json file from 2:06
    the directory on our host to the image. 2:11
    Because we set the working directory to user/src/app earlier in the file, 2:17
    all we have to do is provide a target file name of package.json, and 2:22
    it'll copy the file straight into the app directory. 2:27
    With the package.json file copied over, we'll be able to run NPM. 2:30
    We can execute commands while building an image with the RUN instruction, 2:35
    and we'll run a command of npm install. 2:40
    That'll read the package.json file, see that our app has a dependency 2:42
    on the express web framework, and install it for us. 2:47
    In addition to the package.js file we're of course going to 2:51
    need the file containing the app itself. 2:55
    We can use another copy instruction to copy that over to the working directory, 2:58
    COPY server.js, to a destination file of, 3:03
    server.js, which of course that will take place within, 3:07
    that'll be copied to the user source app directory by default. 3:11
    Our server is going to be running on port 80. 3:16
    So the browsers can connect, 3:18
    we're going to need to expose that port on the container. 3:20
    We do that with the EXPOSE instruction, and we'll expose port 80, 3:22
    and lastly we need to run the server when the container starts up. 3:28
    NPM can use the start instruction in our package.json file to launch the server, 3:33
    but we need to launch NPM. 3:39
    So we'll use the ENTRYPOINT instruction, and that'll set up a command to run. 3:41
    We'll have it run the npm command. 3:49
    And we'll pass an argument of start to npm. 3:54
    We'll save that and that should be all the setup we need. 3:57
    In the next video, we'll build and run the image, and try it out. 4:01

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