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 ande a basic understanding of how a Node.js application is structured.

You can pull the finished code/image from my git/docker hub:

github-logo-icon-30https://github.com/drlukeangel/Docker-Node-Basic-App-Example

 

dockerhub docker images

https://hub.docker.com/r/drlukeangel/basic-node-docker-web-app/

 

 

In the first part of this guide i’ll create a simple web application in Node.js, then i’ll will build a Docker image for that application, and lastly i’ll 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.

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:

Then, create a server.js file that defines a web app using the Express.js framework:

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.

Creating a Dockerfile

Create an empty file called 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:

 

Next we create a directory to hold the application code inside the image, this will be the working directory for your application:

 

 

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:

 

To bundle your app’s source code inside the Docker image, use the COPY instruction:

 

Your app binds to port 8080 so you’ll use the EXPOSE instruction to have it mapped by the docker daemon:

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:

 

Your Dockerfile should now look like this:


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:

 

Your image will now be listed by Docker:

 

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:

 

Print the output of your app:

 

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

 

Test

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

 

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):

Response:

 

 

I 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:

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