How to Build and Deploy a Docker Container

Introduction

Docker has revolutionized software development by making it easier to package, distribute, and deploy applications. Whether you are a developer or a system administrator, understanding how to build and deploy a Docker container is essential. This guide will walk you through the process of creating a Docker container and deploying it to a production environment.

Just like physical shipping containers standardize the transportation of goods, Docker standardizes the deployment of applications across different environments.

Prerequisites

Before you start, ensure you have the following installed on your system:

Docker: Install Docker from Docker's official website.
A Code Editor: VS Code, Sublime Text, or any other text editor.
A Sample Application: A simple Node.js or Python application to containerize.

Step 1: Create a Sample Application

To demonstrate Dockerization, let's create a simple Node.js application.

Initialize a Node.js Project:

mkdir docker-demo && cd docker-demo npm init -y
Install Express:

npm install express
Create server.js file:

const express = require('express'); const app = express(); const PORT = 3000; app.get('/', (req, res) => { res.send('Hello, Docker!'); }); app.listen(PORT, () => { console.log(`Server is running on port ${PORT}`); });

Step 2: Create a Dockerfile

A Dockerfile is a script that contains a set of instructions to create a Docker image. Create a Dockerfile in the project directory and add the following:

# Use official Node.js image
FROM node:14

# Set the working directory
WORKDIR /app

# Copy package.json and install dependencies
COPY package.json .
RUN npm install

# Copy the entire project
COPY . .

# Expose the application port
EXPOSE 3000

# Define the command to run the app
CMD ["node", "server.js"]

Step 3: Build a Docker Image

Once the Dockerfile is ready, we need to build the Docker image. Run the following command in the project directory:

docker build -t my-docker-app .

This command:

docker build instructs Docker to create an image.
-t my-docker-app assigns the name my-docker-app to the image.
. specifies the current directory as the build context.

Step 4: Run the Docker Container

After building the image, we can create and run a container from it:

docker run -p 4000:3000 my-docker-app

-p 4000:3000 maps port 3000 inside the container to port 4000 on your local machine.
my-docker-app is the name of the image.

Now, open a browser and visit http://localhost:4000. You should see Hello, Docker! displayed on the screen.

Step 5: Push the Docker Image to Docker Hub

To deploy the application, we need to store the Docker image in a public or private repository like Docker Hub.

Login to Docker Hub:

docker login -u your-username 2. **Tag the Image:** bash docker tag my-docker-app your-username/my-docker-app:v1 3. **Push the Image:** bash docker push your-username/my-docker-app:v1 ```

Step 6: Deploying the Container to a Cloud Provider

You can deploy the Docker container to various cloud platforms like AWS, Google Cloud, Azure, or DigitalOcean. Below is a simple deployment using Docker Compose.

Using Docker Compose

Create a docker-compose.yml file and add:

version: '3'
services:
  web:
    image: your-username/my-docker-app:v1
    ports:
      - "4000:3000"

Run the application using:

docker-compose up -d

This will run the application in detached mode (-d flag), keeping it running in the background.