<< back to Guides

⚙️ Jenkins Quick Guide

Jenkins is an open-source automation server widely used for CI/CD. It allows developers to build, test, and deploy applications automatically.

---

🔧 Key Concepts

Concept	Description
Job	A task or set of tasks (like build, test, deploy) defined in Jenkins.
Pipeline	A set of steps (stages) written in Groovy DSL to define the workflow.
Agent	A machine (or container) where Jenkins executes jobs.
Executor	A slot for running one job at a time on an agent.
Node	Any machine connected to Jenkins (master or worker).
Workspace	Directory on the node where Jenkins stores files for the job.
Artifact	Files created during a build (e.g., binaries, logs) that are saved/exported.

---

🚀 Freestyle vs Pipeline

• Freestyle Job: Simple GUI-based configuration.
• Pipeline Job: Code-as-configuration using Jenkinsfile with full control and versioning.

---

📝 Jenkinsfile Example (Declarative)

pipeline {
  agent any

  environment {
    APP_ENV = 'development'
  }

  stages {
    stage('Checkout') {
      steps {
        checkout scm
      }
    }

    stage('Build') {
      steps {
        echo 'Building the project...'
      }
    }

    stage('Test') {
      steps {
        echo 'Running tests...'
      }
    }

    stage('Deploy') {
      when {
        branch 'main'
      }
      steps {
        echo 'Deploying to production...'
      }
    }
  }

  post {
    success {
      echo 'Pipeline completed successfully.'
    }
    failure {
      echo 'Pipeline failed.'
    }
  }
}

---

🔄 Trigger Options

Trigger	Description
pollSCM	Periodically check source control for changes.
cron	Run on a schedule.
GitHub Webhook	Trigger on push or pull request.
Manual Trigger	Start pipeline by clicking Build Now.

---

🧰 Plugins to Know

• Git Plugin: Integrates Git SCM.
• Pipeline Plugin: Required for Jenkinsfile support.
• Blue Ocean: Visual interface for pipelines.
• Credentials Binding: For securely managing secrets.
• Docker Pipeline: If you’re building inside containers.
• Slack Notification: For alerts in your team channel.

---

✅ Best Practices

• Use Jenkinsfile in version control.
• Run builds in isolated environments (e.g., Docker).
• Archive build artifacts and test results.
• Use stages for clear separation of concerns.
• Store secrets in Jenkins credentials store.
• Enable build status notifications (Slack, Email).

---

📎 Jenkins Appendix: Docker, Kubernetes, Reusable Libraries, Terraform & Helm Pipelines

---

🐳 Jenkins + Docker

Build and run your app inside Docker containers to ensure environment consistency.

pipeline {
  agent {
    docker {
      image 'node:18-alpine'
      args '-u root:root'
    }
  }

  stages {
    stage('Install') {
      steps {
        sh 'npm install'
      }
    }

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

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

🧠 Note: Requires Docker installed and accessible to Jenkins agent.

---

☸️ Jenkins + Kubernetes (Using Kubernetes Plugin)

Run each stage in a containerized pod using Kubernetes.

pipeline {
  agent {
    kubernetes {
      yaml """
apiVersion: v1
kind: Pod
spec:
  containers:
  - name: maven
    image: maven:3.8.5-openjdk-17
    command:
    - cat
    tty: true
  - name: node
    image: node:18-alpine
    command:
    - cat
    tty: true
"""
    }
  }

  stages {
    stage('Build') {
      steps {
        container('maven') {
          sh 'mvn clean package'
        }
      }
    }

    stage('Test') {
      steps {
        container('node') {
          sh 'npm install && npm test'
        }
      }
    }
  }
}

🔒 Tip: Use Kubernetes service accounts and namespaces for isolation.

---

🔁 Jenkins Shared Library (Reusable Pipelines)

Extract common pipeline logic into shared Groovy libraries stored in a Git repo.

1. Structure of the shared library (in Git):

(root)
└── vars/
    └── deployApp.groovy

2. Content of deployApp.groovy:

def call(String serviceName) {
  pipeline {
    agent any

    stages {
      stage("Build ${serviceName}") {
        steps {
          echo "Building ${serviceName}..."
        }
      }
      stage("Deploy ${serviceName}") {
        steps {
          echo "Deploying ${serviceName} to production..."
        }
      }
    }
  }
}

3. Jenkinsfile using shared library:

@Library('my-shared-library') _

deployApp('orders-service')

🧠 Note: Configure the shared library repo in Manage Jenkins → Configure System → Global Pipeline Libraries

---

🌍 Jenkins + Terraform

Use Jenkins to plan and apply infrastructure changes with Terraform.

pipeline {
  agent any

  environment {
    TF_WORKSPACE = 'prod'
  }

  stages {
    stage('Checkout') {
      steps {
        git 'https://github.com/your-org/terraform-infra-repo.git'
      }
    }

    stage('Terraform Init') {
      steps {
        sh 'terraform init'
      }
    }

    stage('Terraform Plan') {
      steps {
        sh "terraform workspace select ${TF_WORKSPACE} || terraform workspace new ${TF_WORKSPACE}"
        sh 'terraform plan -out=tfplan'
      }
    }

    stage('Terraform Apply') {
      when {
        branch 'main'
      }
      steps {
        input message: 'Approve Terraform apply?'
        sh 'terraform apply tfplan'
      }
    }
  }
}

🔐 Tip: Store Terraform credentials (e.g., AWS, GCP) in Jenkins credentials and inject them into the environment securely.

---

⛵ Jenkins + Helm (for Kubernetes Deployments)

Use Helm in a Jenkins pipeline to deploy applications to Kubernetes clusters.

pipeline {
  agent any

  environment {
    KUBECONFIG = credentials('kubeconfig-jenkins')
  }

  stages {
    stage('Checkout') {
      steps {
        git 'https://github.com/your-org/helm-charts.git'
      }
    }

    stage('Helm Lint') {
      steps {
        dir('my-chart') {
          sh 'helm lint .'
        }
      }
    }

    stage('Helm Dry Run') {
      steps {
        dir('my-chart') {
          sh 'helm upgrade --install my-app . --namespace prod --dry-run'
        }
      }
    }

    stage('Helm Deploy') {
      when {
        branch 'main'
      }
      steps {
        dir('my-chart') {
          sh 'helm upgrade --install my-app . --namespace prod'
        }
      }
    }
  }
}

📦 Tip: Helm dependencies? Run helm dependency update before deploying.

---

<< back to Guides