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In this lesson, you’ll discover how to use Jenkins Shared Libraries to centralize common pipeline logic, reduce duplication, and enforce consistency across all your projects. A Shared Library is a Git-hosted collection of Groovy scripts that define reusable pipeline steps. By abstracting repetitive tasks into library functions, your Jenkinsfiles become cleaner, easier to read, and maintain.
The image is an overview of a "Shared Library," highlighting its benefits: encapsulating common tasks and making pipelines more concise and readable.

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Why Use Shared Libraries?

Imagine maintaining dozens of Jenkinsfiles, each running the same build-and-test steps. You’ll encounter:
  • Duplication: Copy-pasting identical pipeline blocks.
  • Inconsistency: Updates applied to one pipeline aren’t reflected in others.
  • Complexity: Scattering changes across repositories becomes error-prone.
The image is a slide titled "Why use Shared Library" with icons and labels for "Duplication," "Inconsistency," and "Complexity."
Following the DRY (Don’t Repeat Yourself) principle helps you write pipeline logic once and use it everywhere.

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Example: From Hard-Coded to Library-Driven

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Before: Repeating the Welcome Message

// Jenkinsfile (generic)
pipeline {
  agent any
  stages {
    stage('Welcome') {
      steps {
        sh 'echo Welcome to the DevOps team from Dasher Organization'
      }
    }
    stage('Build') {
      steps {
        sh 'npm install'
        sh 'npm run build'
      }
    }
  }
}
Variations for Linux and Windows pipelines simply duplicate that same Welcome step: 
// Jenkinsfile (windows)
pipeline {
  agent { label 'windows' }
  stages {
    stage('Welcome') {
      steps {
        bat 'echo Welcome to the DevOps team from Dasher Organization'
      }
    }
    stage('Checkout') {
      steps {
        checkout scm
      }
    }
  }
}
Updating the organization name to KodeKloud in hundreds of Jenkinsfiles is both time-consuming and risky.

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After: Centralizing the Welcome Step

Move the welcome logic into a shared library function: 
// vars/welcomeMessage.groovy
def call() {
  sh 'echo Welcome to the DevOps team from Dasher Organization'
}
Invoke it in any Jenkinsfile: 
@Library('kode-kloud-shared-library')
pipeline {
  agent any
  stages {
    stage('Welcome') {
      steps {
        welcomeMessage()
      }
    }
    stage('Build') {
      steps {
        sh 'npm install'
        sh 'npm run build'
      }
    }
  }
}
Now a single change in welcomeMessage.groovy updates every pipeline automatically.
The image outlines the steps to create a shared library in Jenkins, including repository setup, Jenkins configuration, writing custom steps, and integrating into pipelines.

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Setting Up Your Shared Library

  1. Create a Git repository dedicated to your shared library.
  2. Configure Jenkins under Manage Jenkins > Configure System > Global Pipeline Libraries: define the library name, default version (branch), and SCM details.
  3. Structure your repo with src/, vars/, and resources/ directories.
  4. Use @Library('your-library-name') in Jenkinsfiles to load and call your custom steps.
The image shows a shared library repository structure with directories for source files, variables, and resources, including Groovy and JSON files.

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Typical Repository Layout

(shared-library-repo)
├── src/                # Optional: compiled Groovy/Java code
├── vars/               # Required: one .groovy per pipeline step
│   ├── welcomeMessage.groovy
│   └── welcomeMessage.txt  # Documentation for the step
└── resources/          # Optional: non-code files (JSON, templates)
DirectoryPurpose
src/Standard Java/Groovy classes (compiled on the classpath)
vars/Each Groovy file defines a pipeline step; filenames use camelCase
resources/Static files loaded via libraryResource

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Configuring Global Pipeline Libraries

In Manage Jenkins > Configure System under Global Pipeline Libraries, add your library:
FieldDescription
Namekode-kloud-shared-library
Default Versionmain (branch or tag)
Retrieval MethodModern SCM (Git) with repository URL
Allow default version to be overriddenEnable if you want to load other branches via @Library
The image shows a configuration screen for "Global Pipeline Libraries" with options for setting a library name, default version, and retrieval method. It includes checkboxes for various settings and a URL for a GitHub repository.
Ensure Jenkins has appropriate read permissions for your Shared Library repository.

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Advanced Example: Notification Utility

Add a reusable notification step in vars/sendNotification.groovy: 
def call(String buildStatus = 'STARTED') {
  buildStatus = buildStatus ?: 'SUCCESS'
  def color, emoji
  if (buildStatus == 'SUCCESS') {
    color = '#47c265'; emoji = ':smile:'
  } else if (buildStatus == 'UNSTABLE') {
    color = '#f39c12'; emoji = ':neutral_face:'
  } else {
    color = '#e74c3c'; emoji = ':boom:'
  }
  // Example: slackSend(color: color, message: "${emoji} Build ${currentBuild.fullDisplayName} is ${buildStatus}")
}
Invoke it in your Jenkinsfile after tests: 
@Library('kode-kloud-shared-library')
pipeline {
  agent any
  stages {
    stage('Build') { steps { sh 'npm install'; sh 'npm run build' } }
    stage('Test')  { steps { sh 'npm test' } }
  }
  post {
    always { sendNotification(currentBuild.currentResult) }
  }
}

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References

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