Jenkins

Jenkins

Jenkins is the most widely used open-source automation server. It enables building, testing, and deploying through plugins and pipeline-as-code with Jenkinsfile.

Jenkins Architecture

  ┌──────────────┐     ┌──────────────┐
  │   Jenkins    │────▶│   Build      │
  │   Master     │     │   Agent 1    │
  │              │────▶│   Agent 2    │
  │  - Schedules │     │   Agent 3    │
  │  - Dashboard │     │              │
  │  - Config    │     │  (Workers)   │
  └──────────────┘     └──────────────┘
       Master-Agent architecture for scalability

Jenkinsfile (Declarative Pipeline)

  pipeline {
      agent any

      stages {
          stage('Checkout') {
              steps {
                  git 'https://github.com/user/app.git'
              }
          }

          stage('Build') {
              steps {
                  sh 'npm install'
                  sh 'npm run build'
              }
          }

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

          stage('Deploy') {
              steps {
                  sh 'docker build -t myapp:latest .'
                  sh 'docker push myapp:latest'
                  sh 'kubectl apply -f k8s/'
              }
          }
      }

      post {
          failure {
              mail to: 'team@example.com',
                   subject: "Build Failed: ${currentBuild.fullDisplayName}"
          }
      }
  }

Key Jenkins Concepts

• Pipeline — Automated workflow defined as code (Jenkinsfile)
• Stages — Logical divisions of the pipeline (Build, Test, Deploy)
• Steps — Individual tasks within a stage
• Agents — Machines that execute the pipeline
• Plugins — 1800+ plugins for integrations (GitHub, Docker, Slack, etc.)