Creating a Docker image for a Javascript application

21 Sep 2023

docker

Docker has revolutionized the way we develop, package, and deploy applications. It provides a lightweight and portable containerization platform that allows developers to package their applications and dependencies into a single, self-contained unit called an image.

In this tutorial, we will walk through the process of creating a Docker image for a JavaScript application. We will cover the basic steps required to set up a Dockerfile, install dependencies, and build the image.

Step 1: Set up the Dockerfile

First, let’s create a file named “Dockerfile” in the root directory of our JavaScript application. The Dockerfile is a text file that contains a set of instructions for building the image.

# Use an official Node.js runtime as the base image
FROM node:14-alpine

# Set the working directory inside the container
WORKDIR /app

# Copy package.json and package-lock.json to the working directory
COPY package*.json ./

# Install dependencies
RUN npm install

# Copy the rest of the application code to the working directory
COPY . .

# Expose a port for your application to listen on (optional)
EXPOSE 3000

# Define the command to run your application
CMD ["npm", "start"]

Let’s go through the Dockerfile step by step:

FROM node:14-alpine sets the base image for our application as the official Node.js runtime version 14, based on the Alpine Linux distribution. You can choose a different Node.js version or a different base image depending on your requirements.
WORKDIR /app sets the working directory inside the container as /app. This will be the root directory for our application.
COPY package*.json ./ copies the package.json and package-lock.json files from the host machine to the working directory inside the container.
RUN npm install installs the application dependencies. This step ensures that all the required dependencies are installed inside the container.
COPY . . copies the rest of the application code from the host machine to the working directory inside the container.
EXPOSE 3000 exposes port 3000, which is commonly used for JavaScript applications. You can change it to the appropriate port for your application.
CMD ["npm", "start"] defines the command to run your application (npm start in this case).

Step 2: Build the Docker Image

To build the Docker image, open a terminal or command prompt, navigate to the root directory of your JavaScript application (where the Dockerfile is located), and run the following command:

docker build -t myapp .

The -t myapp flag tags the image with the name “myapp” (replace it with your desired image name).

Docker will then execute the instructions in the Dockerfile and build the image. This process might take a few moments, especially if it is the first time Docker is downloading the base image and dependencies.

Once the image is built successfully, you can verify its existence by running docker images.

Step 3: Run the Docker Container

To run the Docker container from the image, use the following command:

docker run -p 3000:3000 myapp

The -p 3000:3000 flag maps port 3000 of the Docker container to port 3000 of the host machine. Change it to the appropriate port if necessary.

After running the command, you should see the output of your JavaScript application in the console. You can access your application by opening a web browser and navigating to http://localhost:3000.

Congratulations! You have successfully created a Docker image for your JavaScript application and run it as a container. Docker provides a powerful and flexible way to package and deploy applications, making it easier to maintain consistency across different environments.

#docker #javascript