JENKINS BASIC

⚙️ Jenkins – Complete Core Notes

CI/CD Pipeline Architecture, Declarative Jenkinsfile, Automated Builds, Plugins aur Master-Agent Ecosystem ka comprehensive guide.

1️⃣ Jenkins Kya Hai?

Definition: Jenkins ek leading open-source Java-based automation server hai jiska primary use software development me Continuous Integration (CI) aur Continuous Delivery/Deployment (CD) workflows ko automate karne ke liye kiya jata hai.

CI vs CD Concept:

• CI (Continuous Integration): Developers ke code commit karte hi automatically code checkout, build compilation aur unit tests run karna.
• CD (Continuous Delivery/Deployment): Code tests pass hone ke baad binary artifacts ko automatically Staging ya Production servers par deploy karna.

• Automated Workflows: Manual deployments aur human errors ko eliminate karta hai.
• Vast Ecosystem: 1800+ community plugins ke sahare Git, Docker, Kubernetes, AWS aur Slack ke sath instantly connect hota hai.
• Web Interface: Browser-based intuitive UI provide karta hai jisse build status aur logs monitor karna aasan hota hai.

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2️⃣ Jenkins Ke Core Features

• Pipeline-as-Code: Pura build aur deployment sequence code file (Jenkinsfile) me store hota hai jo version control me track hoti hai.
• Distributed Architecture: Master-Agent (Node) model ke sath builds ko multiple parallel servers par distribute kar sakta hai.
• Extensibility: Custom plugins ke sath kisi bhi programming language ya testing framework ko support karta hai.
• Easy Upgrades: Self-contained Java application hone ke karan single WAR package ya Docker container me easily deploy ho jata hai.

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3️⃣ Installation & Initial Setup

1. Prerequisite: Server par Java (JDK 17 ya 21) install hona mandatory hai.
2. Download & Run: Official packages ya direct Docker container ke zariye start karein:

   docker run -p 8080:8080 -p 50000:50000 -v jenkins_home:/var/jenkins_home jenkins/jenkins:lts

3. Access Dashboard: Browser me open karein: http://localhost:8080
4. Unlock Password: Terminal logs se initial admin password copy karke paste karein:

   sudo cat /var/lib/jenkins/secrets/initialAdminPassword

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4️⃣ Jenkins Jobs: Freestyle vs Pipeline

Job Category	Configuration Style	Best Use-Case
Freestyle Project	Web UI forms aur dropdowns ke through configure hota hai.	Simple single-command tasks, batch scripts ya quick automated testing ke liye.
Pipeline (Declarative)	Jenkinsfile me code ke roop me likha jata hai.	Complex multi-stage CI/CD deployments (Build → Test → Push → Deploy).

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5️⃣ Jenkins Declarative Pipeline (Jenkinsfile)

Industry-standard pipeline structure jisme har stage clear aur isolated hoti hai:

pipeline {
    agent any // Kisi bhi available build agent par run karein

    stages {
        stage('Code Checkout') {
            steps {
                echo 'Checking out code from Git repository...'
            }
        }
        stage('Build & Compile') {
            steps {
                echo 'Running build scripts (e.g., npm install / mvn clean package)...'
            }
        }
        stage('Automated Testing') {
            steps {
                echo 'Executing unit and integration tests...'
            }
        }
        stage('Production Deploy') {
            steps {
                echo 'Deploying artifact to AWS / Kubernetes cluster...'
            }
        }
    }

    post {
        success {
            echo 'Pipeline executed successfully! Notification sent.'
        }
        failure {
            echo 'Build failed! Alert triggered to developer.'
        }
    }
}

Live CI/CD Pipeline Simulator

1. Checkout

2. Build

3. Test

4. Deploy

[Jenkins Console]: Click 'Trigger Build' to simulate automated pipeline execution...

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6️⃣ Essential Production Plugins

Plugin Name	Role in DevOps Pipeline
Git Plugin	GitHub, GitLab ya Bitbucket repos se automated webhooks aur checkout handle karta hai.
Docker Pipeline	Containers build karna aur Docker Hub / ECR par image push karne ka native support deta hai.
Pipeline Stage View	Dashboard par colorful visual blocks ke roop me stage progress display karta hai.
Slack / Email Extension	Build pass ya fail hone par teams ko instant notifications forward karta hai.