What is Jenkins? How to create pipeline using jenkins

 

✅ What is Jenkins? (Simple Explanation for Students)

🔧 Jenkins is a free tool used by developers to automate tasks like:

• Building code

• Testing code

• Deploying applications

💡 Think of Jenkins as a Robot Assistant:

Whenever you write code and push it to GitHub, Jenkins can:

• Automatically test if the code works

• Automatically build the app

• Automatically deploy it to a server

🔁 This process is called CI/CD:

• CI – Continuous Integration (build + test automatically)

• CD – Continuous Deployment (deploy automatically)

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🚀 Jenkins Installation: Key Steps and Important Options

🔷 Windows Installation Steps:

1. Install Java First (JDK)
   Jenkins needs Java to run.

   • Download JDK from Oracle or OpenJDK

   • Set JAVA_HOME environment variable

   • Add Java to system PATH

2. Download Jenkins

   • Go to https://www.jenkins.io

   • Download the Jenkins Windows Installer (.msi)

3. Run Installer

   • Double-click and follow steps

   • It will install Jenkins as a Windows Service

4. Initial Setup

   • Go to http://localhost:8080

   • Unlock Jenkins using the password in the file shown on screen

     • Path: C:\Program Files\Jenkins\secrets\initialAdminPassword

   • Install Suggested Plugins (Recommended)

   • Create Admin User

5. Ready to Use!

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🔷 Linux Installation Steps (Ubuntu/Debian Example):

1. Install Java

   
   sudo apt update
   sudo apt install openjdk-17-jdk -y
   

2. Add Jenkins Repository

   bash
   
   curl -fsSL https://pkg.jenkins.io/debian/jenkins.io-2023.key | sudo tee \
     /usr/share/keyrings/jenkins-keyring.asc > /dev/null
   echo deb [signed-by=/usr/share/keyrings/jenkins-keyring.asc] \
     https://pkg.jenkins.io/debian binary/ | sudo tee \
     /etc/apt/sources.list.d/jenkins.list > /dev/null
   

3. Install Jenkins

   
   sudo apt update
   sudo apt install jenkins -y
   

4. Start Jenkins

   
   sudo systemctl start jenkins
   sudo systemctl enable jenkins
   

5. Open in Browser
   Visit http://your-server-ip:8080

   • Unlock Jenkins with password:

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

   • Install Suggested Plugins

   • Create Admin User

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⭐ Most Important Options in Jenkins (For Beginners):

Feature	What It Does (In Simple Words)
Freestyle Project	Manually configure tasks like build/test/deploy
Pipeline	Write scripts to automate build + deploy
Build Triggers	Run job automatically (e.g. when code is pushed)
Source Code Management (SCM)	Connect with GitHub, GitLab, Bitbucket
Post-build Actions	Send emails, deploy code, etc. after build
Plugins	Add extra features (GitHub, Docker, Slack, etc.)

Task1 create free style project to print hello world under windows machine

Step1 : Open Jenkins

Step2:   NEW ITEM

Step3    Click on Free Style Project

Step4:  Write Description if required

Step5:  Direct go into build steps

Step6:  Select Windows Batch Command if using Windows or Select Linux command

Step7: Write command  echo HelloWorld

step8: Save

Step9: Click on Build if green then pass of red then fail

Step 10: show console output

Task2:  Create Java Program and push into github using git , compile and execute this code under Jenkins using Free Style Project

Note:  Java Environment Path Must be Set in your PC check from command prompt to write java --version

Step1 : Open Jenkins

Step2:   NEW ITEM

Step3    Click on Free Style Project

Step4:  Write Description if required

Step5: Go into settings --> Manage Jenkins ---> Tools---> Configure Tools--> Set git path

Name: Default

Path    C:\Program Files\Git\bin\git.exe

Step6: Again come on Free Style Project

Step7:  go into source code management and set git public repository path

Step8 Come into Build Step Option and write following command

          echo Java Program compilation

         javac HelloWorld.java

         echo Java Program Execution

        java HelloWorld

step9: Click Build now

step 10: Click on Build and Check Console Output and show Java Code Result

Task3:  Create Python Program and push into github using git ,  execute this code under Jenkins using Free Style Project

Note:  Python Environment Path Must be Set in  System Path and Full path like this (C:\Users\Shiva-PC\AppData\Local\Programs\Python\Python313\) your PC check from command prompt to write python --version

Step1 : Open Jenkins

Step2:   NEW ITEM

Step3    Click on Free Style Project

Step4:  Write Description if required

Step5: Go into settings --> Manage Jenkins ---> Tools---> Configure Tools--> Set git path if it is not 

Name: Default

Path    C:\Program Files\Git\bin\git.exe

Step6: Again come on Free Style Project

Step7:  go into source code management and set git public repository path where python code exist

Step8 Come into Build Step Option and write following command

         python filename

step9: Click Build now

step 10: Click on Build and Check Console Output and show Java Code Result

Task4:  Build Execute by Github Webhooks

step1st:  Configure build and select Triggers GitHub hook trigger for GITScm polling

?

step2nd: go into github setting ---> Webhooks Option ---->  and try http://localhost:8080/webhooks

step3: it provide error localhost path not supported

step4:  install ngrok to map localpath to remote path

step5th install and dowload ngrok

1. Install ngrok

Download from: https://ngrok.com/download

Extract and place ngrok.exe in a known location (e.g., C:\ngrok\ngrok.exe)

2. Run ngrok to Expose Jenkins

Open Command Prompt and run:

ngrok http 8080

You’ll see output like:

Forwarding                    http://abc123.ngrok.io -> http://localhost:8080
Forwarding                    https://abc123.ngrok.io -> http://localhost:8080

✅ Copy the HTTPS URL (e.g., https://abc123.ngrok.io)

3) Manage ngrok authentication with login and authenticate token

step6:  replace ngrok url under payload url like this https://d3d61da557f0.ngrok-free.app/github-webhook/

4) choose webhooks triggers 

i choose commit and push both

5) build automatically created when you push or commit in jenkins

Task5:  Build Java Project using Maven from github (Free Style Project)

Before this task first study about maven Maven Tutorials

1)  Upload Maven Project Under github

2)  Create Free Style Project

3)  add github repsoitory and set branch

4) set windows batch command

cd MyFirstMavenProject

mvn clean package

cd target

java -cp MyFirstMavenProject-1.0-SNAPSHOT.jar com.example.App

for execution 

run this 

cd target

java -cp MyFirstMavenProject-1.0-SNAPSHOT.jar com.test.App

📌 What is a Pipeline in Jenkins?

A Jenkins Pipeline is a way to define the steps of your build process as code (written in Groovy).
Instead of clicking around in the Jenkins UI to configure a job, you put all your build steps inside a file called Jenkinsfile.

This gives you:

• Automation (every build runs exactly the same way)

• Version control (the pipeline code lives with your project)

• Flexibility (build, test, deploy in sequence)

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🛠 Simple Jenkins Pipeline Example

groovy

pipeline {
    agent any

    stages {
        stage('Hello') {
            steps {
                echo 'Hello from Jenkins Pipeline!'
            }
        }
    }
}

 Another Jenkins Pipeline Example
pipeline {
    agent any

    stages {
        stage('BUILD') {
            steps {
                echo 'Hello This is for Build'
            }
        }
        stage('TEST') {
            steps {
                echo 'Hello This is for Test!'
            }
        }
        stage('DEPLOY') {
            steps {
                echo 'Hello This is Deploy !'
            }
        }
    }
}

Task6:  Build Java Project using Maven from github (Pipeline Style Project)

1)  create project using maven

2)  push into github repository

3) create jenkinspipelinebuild

4) write this pipleine script

pipeline {

    agent any

    tools {

        maven 'Maven_3.9.6'  // name from Global Tool Config

        jdk 'JDK17'          // name from Global Tool Config

    }

    stages {

        stage('Checkout') {

            steps {

                git branch: 'main', url: 'https://github.com/shivaconceptsolution/MyFirstMavenProject.git'

            }

        }

        stage('Build') {

            steps {

                bat 'mvn clean package'

            }

        }

        stage('Run Application') {

            steps {

                bat 'java -cp target/MyFirstMavenProject-1.0-SNAPSHOT.jar com.test.App'

            }

        }

    }

}

Create complete pipeline to clone code from github, create separate stage to compile , execute java code , execute python code.

pipeline {

    agent any

    stages {

        stage('Clone') {

            steps {

                echo 'Cloning repository...'

                git branch: 'main', url: 'https://github.com/shivaconceptsolution/javasample.git'

            }

        }

        stage('Build') {

            steps {

                echo 'Compiling Java source files...'

                // Use bat for Windows commands

                bat 'javac Hello.java'

            }

        }

        stage('Execute') {

            steps {

                echo 'Running Java program...'

                bat 'java Hello'

            }

        }

        stage('Python Execute') {

            steps {

                echo 'Execute Python Code'

                bat 'python Hello.py'

            }

        }

        stage('Deploy') {

            steps {

                echo 'Hello from Jenkins Pipeline Deployment!'

            }

        }

    }

    post {

        always {

            echo 'Pipeline execution completed.'

        }

    }

}