The goal of this example is to show you how to get a Node.js application into a Docker container. The guide is intended for development, and not for a production deployment. The guide 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 guide 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 software you load into a container.
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_web_app",
"version": "1.0.0",
"description": "Node.js on Docker",
"author": "First Last <[email protected]>",
"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');
const PORT = 8080;
const app = express();
app.get('/', function (req, res) {
res.send('Hello world\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.
Create an empty file called Dockerfile
:
touch Dockerfile
Open the Dockerfile
in your favorite text editor
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 argon
of node
available from the Docker Hub:
FROM node:argon
Next we create a directory to hold the application code inside the image, this will be the working directory for your application:
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:
COPY package.json /usr/src/app/
RUN npm install
To bundle your app's source code inside the Docker image, use the COPY
instruction:
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" ]
Your Dockerfile
should now look like this:
FROM node:argon
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app
COPY package.json /usr/src/app/
RUN npm install
COPY . /usr/src/app
EXPOSE 8080
CMD [ "npm", "start" ]
Go to the directory that has your Dockerfile
and run the following command to
build the Docker image. The -t
flag lets you tag your image so it's easier to
find later using the docker images
command:
$ docker build -t <your username>/node-web-app .
Your image will now be listed by Docker:
$ docker images
REPOSITORY TAG ID CREATED
node argon 539c0211cd76 3 weeks ago
<your username>/node-web-app latest d64d3505b0d2 1 minute ago
Running your image with -d
runs the container in detached mode, leaving the
container running in the background. The -p
flag redirects a public port to a
private port inside the container. Run the image you previously built:
$ docker run -p 49160:8080 -d <your username>/node-web-app
Print the output of your app:
$ docker ps
$ docker logs <container id>
Running on http://localhost:8080
If you need to go inside the container you can use the exec
command:
$ docker exec -it <container id> /bin/bash
To test your app, get the port of your app that Docker mapped:
$ docker ps
ID IMAGE COMMAND ... PORTS
ecce33b30ebf <your username>/node-web-app:latest npm start ... 49160->8080
In the example above, Docker mapped the 8080
port inside of the container to
the port 49160
on your machine.
Now you can call your app using curl
(install if needed via: sudo apt-get
install curl
):
$ curl -i localhost:49160
HTTP/1.1 200 OK
X-Powered-By: Express
Content-Type: text/html; charset=utf-8
Content-Length: 12
Date: Sun, 02 Jun 2013 03:53:22 GMT
Connection: keep-alive
Hello world
We hope this tutorial helped you get up and running a simple Node.js application on Docker.
You can find more information about Docker and Node.js on Docker in the following places: