1. Core Concepts

• Master & Agents: Jenkins can distribute builds across multiple nodes for scalability.
• Pipeline: A sequence of automated steps defined as code to build, test and deploy software.
• Plugins: Extend Jenkins functionality (e.g., GitHub, Docker, Kubernetes, Slack).
• Declarative vs Scripted: Two syntaxes for defining Jenkins pipelines.
• Artifacts & Workspace: Temporary build data and output files generated during jobs.

2. Declarative Pipeline Example

pipeline {
  agent any

  environment {
    DOCKER_IMAGE = "myapp:latest"
  }

  stages {
    stage('Checkout') {
      steps {
        git branch: 'main', url: 'https://github.com/stackcouture/sample-app.git'
      }
    }

    stage('Build') {
      steps {
        sh 'docker build -t $DOCKER_IMAGE .'
      }
    }

    stage('Test') {
      steps {
        sh 'npm test'
      }
    }

    stage('Deploy') {
      steps {
        sh 'docker run -d -p 8080:80 $DOCKER_IMAGE'
      }
    }
  }

  post {
    always {
      echo 'Pipeline complete.'
    }
  }
}

3. Scripted Pipeline Example

node {
  stage('Checkout') {
    git 'https://github.com/stackcouture/sample-app.git'
  }

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

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

  stage('Deploy') {
    sh 'scp target/app.jar ubuntu@server:/opt/app/'
  }

  stage('Notify') {
    echo 'Build and deployment complete.'
  }
}

4. CI/CD Integration Examples

• GitHub Webhooks: Trigger Jenkins builds automatically on push events.
• Docker Integration: Use Docker agents and publish containerized builds.
• Kubernetes: Deploy build agents dynamically using Jenkins Kubernetes plugin.
• Slack Notifications: Send build status updates to Slack channels.

5. Useful CLI & Admin Commands

• Restart Jenkins: sudo systemctl restart jenkins
• List installed plugins: jenkins-cli.jar -s http://localhost:8080/ list-plugins
• Run job via CLI: jenkins-cli.jar -s http://localhost:8080/ build my-job
• Backup config: tar -czf jenkins_backup.tar.gz /var/lib/jenkins