Dockerizing a Node.js web app

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.

示例展示了如何在Docker容器中運行一個Node.js程序,在繼續之前，我們假定你已經有知道如何安裝Docker并且理解Node.js程序是如何組織的。

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 container.

在文檔的第一部分，我們會用Node.js創建一個簡單的web應用程序，之后為這個應用生成一個Docker鏡像，最后將這個鏡像作為容器來運行。

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.

在軟件開發中Docker允許我們將一個程序以及它的所有依賴打包進一個標準化單元——容器，容器是一個只保留了基礎功能的Linux發行版，鏡像是運行在容器中的軟件。

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:

首先，創建一個存放所有項目文件的文件夾，在這個文件夾中創建一個描述它依賴的 package.json 文件：

{
  "name": "docker_web_app",
  "version": "1.0.0",
  "description": "Node.js on Docker",
  "author": "First Last <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:

然后創建一個基于 Express.js 框架的web程序的描述文件：

'use strict';

const express = require('express');

// Constants
const PORT = 8080;

// App
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.

在下一部中我們會看到在使用官方Docker鏡像的容器中運行這個程序，當然，首先我們需要生成一個這個應用的Docker鏡像.

Creating a Dockerfile

Create an empty file called Dockerfile :

創建名為 Dockerfile 的空文件:

touch Dockerfile  

Open the Dockerfile in your favorite text editor

在你喜歡的編輯器中打開 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 argon of node available from the Docker Hub :

我們需要做的第一件事是定義我們從哪個鏡像來構建，在這里我們使用 node 的長期支持版本 argon 來構建，它可以從 Docker Hub 處來獲得：

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:

# 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  

# 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" ]  

Your Dockerfile should now look like this:

FROM node:argon

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

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

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

EXPOSE 8080  
CMD [ "npm", "start" ]  

Building your image

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

# Example
REPOSITORY                      TAG        ID              CREATED  
node                            argon      539c0211cd76    3 weeks ago  
<your username>/node-web-app    latest     d64d3505b0d2    1 minute ago  

Run the image

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:

# Get container ID
$ docker ps

# Print app output
$ docker logs <container id>

# Example
Running on http://localhost:8080  

If you need to go inside the container you can use the exec command:

# Enter the container
$ docker exec -it <container id> /bin/bash

Test

To test your app, get the port of your app that Docker mapped:

$ docker ps

# Example
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:

• Official Node.js Docker Image
• Official Docker documentation
• Docker Tag on StackOverflow
• Docker Subreddit
• Build your own images