• Automating the process of compiling code to produce software (e.g., creating .exe files for Windows or .jar files for Java).
• Jenkins automatically performs this every time you make changes to your code.

• Imagine you’re writing a Java program. Normally, you would run javac and java commands manually. Jenkins automates this by:
1.  Fetching your code from GitHub.
2.  Running a tool like Maven to compile it.
3.  Producing a ready-to-use software file.

• Objective: Automatically compile and build a Java application whenever code is pushed.
• Setup:
1.  Install the Git plugin to pull the code.
2.  Use Maven or Gradle as a build tool.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Checkout') {
        steps {
            git branch: 'main', url: 'https://github.com/your-repo.git'
        }
    }
    stage('Build') {
        steps {
            sh 'mvn clean package'
        }
    }
}

• Outcome: Produces a JAR/WAR file for deployment.

• Ensures your program works as intended by automatically running tests.
• These tests check if your program behaves correctly for different inputs.

• Suppose your program calculates discounts:
• Input: price = 100, discount = 10%
• Expected Output: 90
• Jenkins runs a script to check if your program calculates this correctly every time you make changes.

• Objective: Run tests automatically after every build.
• Setup:
1.  Add test execution and result publishing to your pipeline.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Build') {
        steps {
            sh 'mvn clean install'
        }
    }
    stage('Test') {
        steps {
            sh 'mvn test'
            junit '**/target/surefire-reports/*.xml'
        }
    }
}

• Outcome: Tests are run, and results are published in Jenkins.

• Jenkins uses tools like SonarQube to check your code for mistakes, bad practices, or inefficiencies.

• Imagine your code is full of unnecessary lines or errors. Jenkins will highlight:
• Unused variables.
• Functions that could be written better.
• This ensures you write clean, efficient code.

• Objective: Perform static code analysis to ensure quality.
• Setup:
1.  Install the SonarQube Scanner plugin.
2.  Add a SonarQube analysis stage to your pipeline.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Code Analysis') {
        steps {
            withSonarQubeEnv('SonarQube') {
                sh 'mvn sonar:sonar'
            }
        }
    }
}

• Outcome: Reports code quality metrics in SonarQube.

• Stores files created after building your program (called artifacts) so they can be used later.

• After Jenkins creates a .jar file (Java app), it uploads it to a storage service like Nexus. This makes it easy for others to download and use your program.

• Objective: Store build artifacts for future use.
• Setup:
1.  Use the Nexus Artifact Uploader plugin.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Build') {
        steps {
            sh 'mvn clean package'
        }
    }
    stage('Upload Artifact') {
        steps {
            nexusArtifactUploader(
                nexusVersion: 'nexus3',
                nexusUrl: 'http://nexus.example.com',
                repository: 'maven-releases',
                credentialsId: 'nexus-credentials',
                artifacts: [[
                    artifactId: 'app',
                    file: 'target/app.jar',
                    type: 'jar'
                ]]
            )
        }
    }
}

• Outcome: Artifacts are stored in Nexus.

• Runs the Jenkins job inside a lightweight, isolated container (like a mini-computer) to ensure consistency.

• If Jenkins runs your Java program on Windows, but your teammate uses Linux, the program may behave differently. Using Docker ensures it runs the same everywhere.

• Objective: Isolate build environments.
• Setup: Use the Docker Pipeline plugin.
• Pipeline Example:

    •.      pipeline {
agent {
    docker {
        image 'maven:3.8.1-jdk-11'
    }
}
stages {
    stage('Build') {
        steps {
            sh 'mvn clean install'
        }
    }
}

• Outcome: Builds run in Docker containers.

• Automatically creates separate pipelines for each Git branch. Each branch can have its own rules.

• You might have two branches: main (stable) and dev (work-in-progress). Jenkins ensures code in dev doesn’t break the stable code in main.

• Objective: Automate pipelines for multiple branches.
• Setup: Use Multibranch Pipeline jobs.
• Pipeline Code: Same logic is applied per branch.

• Sends updates about your build (success or failure) to your team via email, Slack, etc.

• If the build fails, Jenkins can send you a message:

• Objective: Notify the team of build results.
• Setup:
1.  Install the Slack Notification plugin.
2.  Configure Slack webhooks.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Build') {
        steps {
            sh 'mvn clean install'
        }
    }
}
post {
    success {
        slackSend(channel: '#dev', message: 'Build succeeded!')
    }
    failure {
        slackSend(channel: '#dev', message: 'Build failed!')
    }
}

• Outcome: Teams are notified on Slack.

• Jenkins automatically deploys your application after building and testing it successfully.

• Your program is uploaded to a Kubernetes cluster or server where users can access it instantly.

• Objective: Deploy applications to Kubernetes after successful builds.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Deploy') {
        steps {
            sh 'kubectl apply -f deployment.yaml'
        }
    }
}

• Validates the scripts used to set up servers (e.g., Terraform files).

• Before creating a cloud server, Jenkins checks if your configuration file is correct to prevent errors during server setup.

• Objective: Validate Terraform configurations.
• Pipeline Example:

• Updates your database (e.g., adding a new column) automatically when you update your application.

• If you add a new feature that needs an extra database column, Jenkins uses tools like Flyway to add the column without breaking the existing database.

• Objective: Automate database schema updates.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Database Migration') {
        steps {
            sh 'flyway migrate'
        }
    }
}

• Deploys your new application version to a small group of users while the rest continue using the old version.

• Imagine you’re updating a website. Only 10% of users see the new version. If it works fine, you roll it out to everyone.

• Objective: Safely deploy without downtime.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Deploy to Blue') {
        steps {
            sh 'aws deploy ...'
        }
    }
}

• Jenkins checks your application for security vulnerabilities using tools like OWASP ZAP.

• Jenkins might scan your website and warn:

• Objective: Check for vulnerabilities.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Security Scan') {
        steps {
            sh 'zap-cli start'
            sh 'zap-cli scan http://app'
        }
    }
}

• Tests your web app on different browsers (e.g., Chrome, Firefox) to ensure it works everywhere.

• If your website looks good on Chrome but breaks on Firefox, Jenkins catches this issue by running tests on all browsers.

• Objective: Test web apps across browsers.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Cross-Browser Tests') {
        steps {
            sh 'selenium-side-runner test.side'
        }
    }
}

• Builds your program for multiple operating systems (Windows, Mac, Linux) in one go.

• You’re creating a game. Jenkins creates .exe (Windows), .dmg (Mac), and .appimage (Linux) files simultaneously.

• Objective: Build for multiple OS environments.
• Pipeline Example:

    •.      pipeline {
agent any
stages {
    stage('Build Linux') {
        steps {
            sh './build-linux.sh'
        }
    }
    stage('Build Windows') {
        steps {
            bat 'build-windows.bat'
        }
    }
}

• Automates tasks like validating datasets and training models for machine learning projects.

• If you’re building an AI model, Jenkins:
1.  Checks if the input data is valid.
2.  Automatically trains the model using this data.

• Objective: Automate ML pipelines.
• Pipeline Example:

    •    pipeline {
agent any
stages {
    stage('Data Validation') {
        steps {
            sh 'python validate_data.py'
        }
    }
    stage('Train Model') {
        steps {
            sh 'python train_model.py'
        }
    }
}

• Think of Jenkins as your assistant.