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This guide covers Docker installation and the critical permission configuration required for Jenkins to build and run Docker containers.

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Overview

Docker is used to containerize the Node.js application. The Jenkins user needs proper permissions to execute Docker commands as part of the CI/CD pipeline.

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Install Docker

1

Update Package Index

sudo apt update
2

Install Prerequisites

Install packages to allow apt to use a repository over HTTPS:
sudo apt install apt-transport-https ca-certificates curl software-properties-common -y
3

Add Docker's GPG Key

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
4

Add Docker Repository

echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
5

Install Docker Engine

sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io -y
6

Verify Installation

Check that Docker is installed correctly:
sudo docker --version
sudo docker run hello-world

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Configure Docker Permissions for Jenkins

This is a critical step. Without proper permissions, Jenkins will fail to execute Docker commands in the pipeline.
The Jenkins user must be added to the Docker group to execute Docker commands without sudo privileges.
1

Add Jenkins to Docker Group

Run the following command to add the jenkins user to the docker group:
sudo usermod -aG docker jenkins
This command modifies the user (usermod) and appends (-aG) the jenkins user to the docker group.
2

Restart Jenkins

Restart the Jenkins service for the changes to take effect:
sudo systemctl restart jenkins
3

Verify Permissions

Verify that the Jenkins user can run Docker commands:
sudo -u jenkins docker ps
If successful, you should see a list of running containers (or an empty list if no containers are running).
If you encounter permission issues, you may need to restart the Docker daemon:
sudo systemctl restart docker
sudo systemctl restart jenkins

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Understanding the Dockerfile

The project uses a Dockerfile to containerize the Node.js application. Here’s the breakdown: 
FROM node:18-alpine

# Set working directory
WORKDIR /app

# Copy files
COPY package*.json ./
RUN npm install
COPY . .

# Expose port
EXPOSE 3000

# Run app
CMD ["node", "index.js"]

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Key Components

  • Base Image: node:18-alpine - Lightweight Node.js 18 image
  • Working Directory: /app - All commands execute in this directory
  • Dependencies: Install npm packages before copying source code (layer caching optimization)
  • Port: Exposes port 3000 (mapped to port 80 during deployment)
  • Command: Runs node index.js to start the application

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Pipeline Usage

The Jenkins pipeline uses Docker in the following stages:

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Build Stage

stage('Build') {
    steps {
        echo 'Building Docker image...'
        sh 'docker build -t $IMAGE_NAME:latest .'
        echo 'Docker image built successfully!'
    }
}

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Deploy Stage

stage('Deploy') {
    steps {
        echo 'Deploying Docker container...'
        sh 'docker run --name Jenkins -d -p 80:3000 $IMAGE_NAME:latest'
        echo 'App deployed on port 80!'
    }
}
The image name is defined as an environment variable: IMAGE_NAME = 'nodejs-demo-app'

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Next Steps

With Docker configured, proceed to GitHub Integration to set up automated builds triggered by code commits.

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