Docker is an open platform for developers and sysadmins to build, ship, and run distributed applications. Consisting of Docker Engine, a portable, runtime-independent application environment, and Docker Hub, a cloud service for sharing applications and automating workflows, Docker enables apps to be quickly assembled from components and eliminates the friction between development, QA, and production environments. As a result, IT can ship faster and run the same app, unchanged, on laptops, data center VMs, and any cloud.
Dockerizing your Node.js applications provides a number of benefits:
Isolation: Containers isolate your application from other applications running on the same host. This makes it easier to run multiple applications on the same host and to ensure that your application has the required libraries and configuration.
Reproducibility: A Docker image contains all the information that is required to run an application. This makes it easy to share applications with other developers and to deploy them in different environments.
Efficiency: By packaging all the dependencies required to run an application in a container, you can avoid installing these dependencies on every host where the application is deployed.
Flexibility: A Docker image can be run on any host that has a Docker runtime. This makes it easy to deploy applications in hybrid environments, such as on-premises data centers and cloud-based platforms.
In this article, we will show you how to dockerize a Node.js application. We will use the Express web framework to build a simple web application and will package it in a Docker image.
Before you begin, you will need the following:
A text editor. We recommend using Visual Studio Code.
Node.js installed on your development machine.
Docker installed on your development machine.
We will start by creating a simple Node.js application using the Express web framework. Create a new directory for your project and initialize a Node.js project in it:
mkdir nodejs-docker
cd nodejs-docker
npm init
You will be prompted to enter information about your project, such as the name, version, description, etc. You can accept the default values by pressing Enter.
Next, install the Express web framework and other dependencies:
npm install express --save
Create a file named app.js in your project directory and add the following code to it:
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('Hello, world!');
});
app.listen(3000, () => {
console.log('Example app listening on port 3000!');
});
This code creates a simple web server that listens on port 3000 and returns the string "Hello, world!" when you make a request to the root URL of the server.
You can start the web server by running the following command:
node app.js
You can then access the web server at http://localhost:3000.
A Dockerfile is a text file that contains the instructions for building a Docker image. Create a file named Dockerfile in your project directory and add the following content to it:
FROM node:alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["node", "app.js"]
This Dockerfile uses the Node.js Alpine image as the base image for our Docker image. The Alpine image is a small Linux distribution that contains the bare minimum required to run a Node.js application.
The WORKDIR instruction sets the working directory for the subsequent instructions. The COPY instruction copies the package.json and package-lock.json files from the project directory to the working directory. The RUN instruction runs the npm install command to install the dependencies for the application. The COPY instruction then copies the rest of the files from the project directory to the working directory. The EXPOSE instruction exposes port 3000. The CMD instruction specifies the command to run when the container is started.
Now that we have created the Dockerfile, we can build the Docker image. Run the following command in your project directory:
docker build -t nodejs-docker .
This command will create a Docker image with the name nodejs-docker.
We can now run the Docker image as a container. Run the following command to start the container:
docker run -d -p 3000:3000 nodejs-docker
This command will start the container and bind port 3000 on the host to port 3000 in the container. The -d option tells Docker to run the container in detached mode. This means that the container will run in the background and the console will return to the command prompt.
You can now access the web server at http://localhost:3000.