🚀 What is Jenkins?

Jenkins is an open-source automation server written in Java. It is used to automate parts of software development, including building, testing, and deploying code.

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🔧 Jenkins Installation

On Ubuntu/Debian:

sudo apt update
sudo apt install openjdk-11-jdk -y
wget -q -O - https://pkg.jenkins.io/debian-stable/jenkins.io.key | sudo apt-key add -
sudo sh -c 'echo deb https://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list'
sudo apt update
sudo apt install jenkins -y
sudo systemctl start jenkins
sudo systemctl enable jenkins

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👥 Jenkins: Creating Users, Jobs, and Master-Slave Configuration

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✅ Creating Users in Jenkins

Jenkins allows multiple users to access and manage jobs securely.

Steps:

1. Go to Manage Jenkins > Manage Users.
2. Click on Create User.
3. Fill in the following details:
   • Username
   • Password
   • Full name
   • Email
4. Click Create User.

🔐 You must have Matrix-based security or Role-based authorization enabled to manage users.

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⚙️ Creating Jobs in Jenkins

Jenkins Jobs are tasks like building a project, running tests, deploying apps, etc.

Steps to Create a Job:

1. From Jenkins Dashboard, click New Item.
2. Enter a job name.
3. Choose a type:
   • Freestyle Project (GUI-based)
   • Pipeline (Scripted)
   • Multi-configuration Project (for matrix builds)
4. Click OK.
5. Configure the job:
   • Source Code Management: Git, SVN, etc.
   • Build Triggers: SCM polling, schedule, webhook
   • Build Steps: Shell commands, Maven, Gradle, etc.
   • Post-build Actions: Email notifications, archiving, etc.
6. Click Save.

📌 Once saved, you can click Build Now to run the job.

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🔗 Configuring Jenkins Master-Slave Architecture

Jenkins supports a distributed build architecture with Master and Slave (Agent) nodes.

💡 Why Use Master-Slave?

• Distribute builds across multiple machines.
• Reduce load on master.
• Run jobs in parallel.
• Run jobs in specific environments (labels/tags).

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🧱 Master:

• Central Jenkins server.
• Manages UI, job scheduling, result tracking.
• Can also execute jobs.

⚙️ Slave (Agent):

• Remote machine connected to Master.
• Executes jobs as per Master's instruction.

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🔧 Steps to Configure Master-Slave:

1. Go to Manage Jenkins > Manage Nodes and Clouds.
2. Click on New Node.
3. Give a name, select Permanent Agent, and click OK.
4. Fill in:
   • Remote root directory (e.g., /home/jenkins)
   • Labels (e.g., linux, build, test)
   • Launch method:
     • SSH
     • Java Web Start (deprecated)
     • Custom launcher
5. Save the node.
6. Jenkins will attempt to connect to the slave machine and establish communication.

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🛠 Requirements on Slave:

• Java should be installed.
• Jenkins master must be able to SSH into slave.

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🔍 Verify:

• Node status will show as Connected and Idle if configured correctly.
• Use labels to bind jobs to specific slaves.

⚠️ Ensure port 50000 (JNLP) or SSH port is open between master and slave for communication.

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🚀 Jenkins Pipelines, Jenkinsfiles, and Git Integration

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🛠 Creating Pipelines in Jenkins

Jenkins Pipeline is a suite of plugins that supports implementing continuous delivery pipelines as code.

🔹 Types of Pipelines:

• Declarative: Simpler, structured syntax
• Scripted: More flexible, Groovy-based

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✅ Steps to Create a Pipeline:

1. From Jenkins Dashboard → Click New Item.
2. Enter a name and select Pipeline.
3. Click OK.
4. In the configuration:
   • Add description (optional).
   • Under Pipeline, choose:
     • Pipeline script (inline)
     • Or Pipeline script from SCM (Git repo).
5. Write or paste your pipeline code (Jenkinsfile).
6. Save and click Build Now to execute.

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🧾 Example Declarative Pipeline:

pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                echo 'Building the application...'
            }
        }
        stage('Test') {
            steps {
                echo 'Running tests...'
            }
        }
        stage('Deploy') {
            steps {
                echo 'Deploying the app...'
            }
        }
    }
}

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🔗 Git Integration with Jenkins

Integrating Git with Jenkins enables version-controlled CI/CD pipelines and seamless automation with your source code.

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📦 Step-by-Step Git Integration

1️⃣ Install Git Plugin in Jenkins

The Git Plugin is required to enable Git SCM features in Jenkins.

🔧 How to Install:

• Navigate to: Manage Jenkins → Manage Plugins
• Go to the Available tab
• Search for: Git plugin
• Click Install without restart

🔄 You can also check the Installed tab to verify if Git plugin is already installed.

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2️⃣ Configure Global Git Settings

Jenkins needs to know the location of the Git binary on the system.

• Go to: Manage Jenkins → Global Tool Configuration
• Under Git, click Add Git
• Name it (e.g., Default Git)
• Let Jenkins auto-detect the path OR manually set the Git executable path (like /usr/bin/git)

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3️⃣ Create Jenkins Job with Git Integration

For Freestyle Projects:

• Go to New Item → Enter job name → Select Freestyle Project
• Under Source Code Management, choose Git
• Enter:
  • Repository URL (e.g., https://github.com/user/repo.git)
  • Branch to build (default is */main or */master)
  • Credentials (if it’s a private repo)

For Pipeline Jobs:

Use Git inside the Jenkinsfile like this:

pipeline {
  agent any
  stages {
    stage('Checkout') {
      steps {
        git branch: 'main', url: 'https://github.com/user/repo.git'
      }
    }
  }
}

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🔐 Managing Git Credentials in Jenkins

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📥 Where to Add Credentials

• Navigate to: Manage Jenkins → Credentials
• Choose the appropriate domain (e.g., Global)
• Click Add Credentials

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🧾 Types of Credentials

Type	Description
Username/Password	For HTTPS Git URLs requiring a username and password
SSH Username with Private Key	For Git over SSH (e.g., GitHub using SSH key)
Secret Text	For personal access tokens (PAT)
Certificate	For advanced use-cases involving cert-based auth

🎯 Use Secret Text if you're integrating GitHub using a Personal Access Token (PAT) for enhanced security.

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🛠 Using Credentials in Jenkins Job

• When configuring Git in Freestyle or Pipeline job, select the appropriate credentialsId.
• Example in Jenkinsfile:

git url: 'https://github.com/user/repo.git', credentialsId: 'github-token-id'