docker-intro.md

Docker Introduction

This exercise walks through:

1. installing Docker
2. grasping Docker fundamentals
3. deploying a static website inside a Docker container

What is Docker?

Docker is an awesome tool we can use to deploy production systems. It allows us to isolate our code in completely clean system environments. The Dockerfile is a sort of installation 'recipe' that can be used to initialize a system environment. A Docker container is a fresh Linux environment that bootstraps from a host systems Linux kernel - this gives us a lot of the benefits of the VM but without the slow execution and bulk often associated with VMs.

Installation

If you are Linux (Ubuntu), follow https://docs.docker.com/installation/ubuntulinux/

If you are on Mac OS X, follow https://docs.docker.com/installation/mac/

Alternatively, see Docker's list of installation guides here.

If any software listed in the guides is already installed on your system, you can of course skip those steps.

Basic knowledge of Docker

Let's do a quick sanity check:

$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES

Docker hasn't complained so we're good to go, the output shows that we have no containers running. Don't worry, we'll build one shortly.

Run Node.js in a Docker container

The following command will start a Node REPL inside a Docker container

$ docker run -it --rm node node

This command pulls in the official node image from the Docker hub and tells Docker to open an interactive terminal into the container and runs the node executable, thus giving us the Node REPL.

Our static website on Docker

Project Setup

First let's create a new directory and initialize a new git repo inside it:

$ mkdir mystatic
$ cd mystatic
$ git init

Sample Application

Let's use the canonincal Node.js web server example:

var http = require('http');
var port = process.env.PORT || 1337;
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(port);
console.log('Server running on port', port);

We'll save that in a file named app.js.

We can test it in the usual way:

$ node app.js

Then in another shell:

$ curl http://localhost:1337

Dockerize!

Now we're going to build a container around the web server.

To get started we need a recipe list: the Dockerfile:

# The world-famous node.js hello world
#
# VERSION 0.0.1

FROM node
MAINTAINER Spongebob

ADD ./ /src

EXPOSE 1337

ENTRYPOINT ["node", "/src/app.js"]

We can build it by typing:

$ docker build .

Which will eventually output:

Successfully built <containerid>

Next we run our container with:

docker run -p 80:1337 <containerid>

(copy paste the container id from the previous command)

Finally we can make a request to our container, in another shell.

If we're using OS X we're using boot2docker which is actually a Linux VM, we need to use the $DOCKER_HOST environment variable to access the VM's localhost.

$ curl http://$(boot2docker ip):80

Otherwise, if we're using Linux we simply request localhost:

$ curl http://localhost:80

Here's one we made earlier: https://github.com/nearform/nscale-workshop-intro-docker-sample

Next up: nscale intro