Jenkins¶

Overview¶

Jenkins is an open-source automation server used to build, test, and deploy software continuously. It enables teams to practice Continuous Integration and Continuous Deployment (CI/CD).

Core Concepts¶

Pipeline vs Freestyle Jobs¶

Aspect	Freestyle	Pipeline
Definition	UI configuration	Code-based (Jenkinsfile)
Version Control	Manual	Stored in Git
Reusability	Limited	High
Debugging	Difficult	Easy
Scalability	Limited	Excellent

Jenkins Architecture¶

┌─────────────────────────────────┐
│      Jenkins Master             │
│  - Job Orchestration            │
│  - Web UI                       │
│  - Plugin Management            │
└──────────────┬──────────────────┘
               │
     ┌─────────┼─────────┐
     │         │         │
   Agent1    Agent2    Agent3
  (Linux)   (Windows) (Docker)

Installation & Setup¶

Docker Installation¶

# Pull Jenkins image
docker pull jenkins/jenkins:lts

# Run Jenkins container
docker run -d -p 8080:8080 -p 50000:50000 \
  -v jenkins_home:/var/jenkins_home \
  --name jenkins \
  jenkins/jenkins:lts

# Get initial admin password
docker exec jenkins cat /var/jenkins_home/secrets/initialAdminPassword

Linux Installation¶

# Update package manager
sudo apt update

# Install Java
sudo apt install -y openjdk-11-jdk

# Add Jenkins repository
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'

# Install Jenkins
sudo apt update
sudo apt install -y jenkins

# Start Jenkins
sudo systemctl start jenkins
sudo systemctl enable jenkins

Pipeline Basics¶

Declarative Pipeline¶

pipeline {
    agent any

    triggers {
        githubPush()  // Trigger on GitHub push
    }

    environment {
        APP_NAME = 'MyApp'
        VERSION = '1.0.0'
        DOCKER_REGISTRY = 'docker.io'
    }

    options {
        buildDiscarder(logRotator(numToKeepStr: '10'))
        timeout(time: 1, unit: 'HOURS')
    }

    stages {
        stage('Checkout') {
            steps {
                echo 'Checking out code...'
                checkout scm
            }
        }

        stage('Build') {
            steps {
                echo 'Building application...'
                sh 'mvn clean package'
            }
        }

        stage('Test') {
            steps {
                echo 'Running tests...'
                sh 'mvn test'
                junit 'target/surefire-reports/*.xml'
            }
        }

        stage('SonarQube Analysis') {
            steps {
                echo 'Running code quality scan...'
                sh 'mvn sonar:sonar'
            }
        }

        stage('Build Docker Image') {
            steps {
                echo 'Building Docker image...'
                sh 'docker build -t ${DOCKER_REGISTRY}/${APP_NAME}:${VERSION} .'
            }
        }

        stage('Push to Registry') {
            steps {
                echo 'Pushing image to registry...'
                sh 'docker push ${DOCKER_REGISTRY}/${APP_NAME}:${VERSION}'
            }
        }

        stage('Deploy to Dev') {
            steps {
                echo 'Deploying to development...'
                sh 'kubectl set image deployment/myapp myapp=${DOCKER_REGISTRY}/${APP_NAME}:${VERSION} -n dev'
            }
        }

        stage('Deploy to Prod') {
            when {
                branch 'main'
            }
            steps {
                echo 'Deploying to production...'
                input 'Approve production deployment?'
                sh 'kubectl set image deployment/myapp myapp=${DOCKER_REGISTRY}/${APP_NAME}:${VERSION} -n prod'
            }
        }
    }

    post {
        always {
            echo 'Cleaning up...'
            cleanWs()
        }
        success {
            echo 'Pipeline succeeded!'
            // Send success notification
        }
        failure {
            echo 'Pipeline failed!'
            // Send failure notification
        }
    }
}

Scripted Pipeline¶

node {
    try {
        stage('Checkout') {
            checkout scm
        }

        stage('Build') {
            sh 'mvn clean package'
        }

        stage('Test') {
            sh 'mvn test'
        }

        stage('Deploy') {
            sh './deploy.sh'
        }
    }
    catch (Exception e) {
        echo "Build failed: ${e.message}"
        throw e
    }
}

Essential Plugins¶

Plugin	Purpose	Use Case
GitHub	SCM integration	Git repositories
Docker	Container management	Build & push images
Kubernetes	K8s integration	Deploy to Kubernetes
SonarQube	Code quality	Quality gates
Slack	Notifications	Team notifications
Email	Email alerts	Build notifications
JUnit	Test reporting	Test result parsing
Artifactory	Artifact storage	Artifact management

Jenkins Credentials¶

Types of Credentials¶

pipeline {
    agent any

    environment {
        // Use credentials plugin
        DOCKER_CREDS = credentials('docker-credentials')
        GIT_TOKEN = credentials('github-token')
    }

    stages {
        stage('Authenticate') {
            steps {
                sh '''
                    echo $DOCKER_CREDS_PSW | docker login -u $DOCKER_CREDS_USR --password-stdin
                '''
            }
        }
    }
}

Store Credentials¶

// Jenkins Credentials UI: Manage Jenkins → Manage Credentials

// Use in pipeline:
withCredentials([
    usernamePassword(
        credentialsId: 'docker-creds',
        usernameVariable: 'DOCKER_USER',
        passwordVariable: 'DOCKER_PASS'
    )
]) {
    sh 'echo $DOCKER_PASS | docker login -u $DOCKER_USER --password-stdin'
}

Integration Examples¶

GitHub Webhook Trigger¶

pipeline {
    agent any

    triggers {
        githubPush()
    }

    stages {
        stage('Pull Code') {
            steps {
                checkout([
                    $class: 'GitSCM',
                    branches: [[name: '*/main']],
                    userRemoteConfigs: [[
                        url: 'https://github.com/user/repo.git'
                    ]]
                ])
            }
        }
    }
}

Docker Integration¶

pipeline {
    agent any

    stages {
        stage('Build and Push') {
            steps {
                script {
                    docker.withRegistry('https://docker.io', 'docker-credentials') {
                        def app = docker.build("myapp:${BUILD_NUMBER}")
                        app.push("latest")
                    }
                }
            }
        }
    }
}

Kubernetes Deployment¶

pipeline {
    agent any

    stages {
        stage('Deploy') {
            steps {
                withKubeConfig([credentialsId: 'kubeconfig']) {
                    sh 'kubectl apply -f deployment.yaml'
                    sh 'kubectl rollout status deployment/myapp'
                }
            }
        }
    }
}

Job Configuration¶

Job Types¶

Type	Use Case	Benefit
Pipeline	Complex workflows	Code-based, version controlled
Freestyle	Simple tasks	Easy to configure
Multibranch	Multiple branches	Branch-specific builds
Folder	Organization	Logical grouping

Common Parameters¶

pipeline {
    agent any

    parameters {
        string(
            name: 'ENVIRONMENT',
            defaultValue: 'dev',
            description: 'Deployment environment'
        )
        choice(
            name: 'VERSION',
            choices: ['1.0.0', '1.0.1', '1.1.0'],
            description: 'Application version'
        )
        booleanParam(
            name: 'RUN_TESTS',
            defaultValue: true,
            description: 'Run tests'
        )
    }

    stages {
        stage('Deploy') {
            steps {
                echo "Deploying version ${params.VERSION} to ${params.ENVIRONMENT}"
                echo "Run tests: ${params.RUN_TESTS}"
            }
        }
    }
}

Monitoring & Logging¶

View Logs¶

# Jenkins logs location
sudo journalctl -u jenkins -f

# Docker Jenkins logs
docker logs -f jenkins

# Workspace logs
/var/lib/jenkins/jobs/JobName/builds/1/log

Health Check¶

# Check Jenkins status
curl http://localhost:8080/api/json

# Verify plugins
curl http://localhost:8080/pluginManager/api/json

# Check nodes
curl http://localhost:8080/computer/api/json

Best Practices¶

Practice	Benefit	Implementation
Use Jenkinsfile	Version control	Store in Git repo
Declarative syntax	Readability	Avoid scripted when possible
Secure credentials	Security	Use credential plugin
Parallel stages	Performance	Reduce build time
Build artifacts	Reusability	Archive outputs
Build history	Troubleshooting	Keep logs
Notifications	Awareness	Slack, email alerts
Test reports	Quality	Publish test results

Troubleshooting¶

Common Issues¶

# Jenkins won't start
sudo systemctl status jenkins
sudo tail -f /var/log/jenkins/jenkins.log

# Out of memory
# Increase JVM heap: JAVA_ARGS="-Xmx2g"

# Slow builds
# Check agent connectivity, add more agents

# Plugin conflicts
# Disable plugin, restart Jenkins

Summary Table: Pipeline Stages¶

Stage	Purpose	Command
Checkout	Get source code	`checkout scm`
Build	Compile code	`mvn clean package`
Test	Run tests	`mvn test`
Analysis	Code quality	`mvn sonar:sonar`
Publish	Create artifact	`docker build`
Deploy Dev	Deploy to dev	`kubectl apply`
Approval	Manual gate	`input 'Approve?'`
Deploy Prod	Deploy to production	`kubectl apply`

Jenkins¶

Overview¶

Core Concepts¶

Pipeline vs Freestyle Jobs¶

Jenkins Architecture¶

Installation & Setup¶

Docker Installation¶

Linux Installation¶

Pipeline Basics¶

Declarative Pipeline¶

Scripted Pipeline¶

Essential Plugins¶

Jenkins Credentials¶

Types of Credentials¶

Store Credentials¶

Integration Examples¶

GitHub Webhook Trigger¶

Docker Integration¶

Kubernetes Deployment¶

Job Configuration¶

Job Types¶

Common Parameters¶

Monitoring & Logging¶

View Logs¶

Health Check¶

Best Practices¶

Troubleshooting¶

Common Issues¶

Summary Table: Pipeline Stages¶

Resources¶