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Jenkins Shared Libraries enable teams to centralize reusable Groovy scripts and pipeline logic in a single, version-controlled repository. By defining common steps—such as notifications, build commands, or deployment tasks—you can apply the DRY principle, reduce duplication, and ensure consistency across all your CI/CD pipelines.
The image is an overview of a "Shared Library," highlighting its benefits: encapsulating common tasks and making pipelines more concise and readable.
Consider a typical Jenkinsfile for a Node.js project: 
pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        sh 'npm install'
        sh 'npm run build'
      }
    }
    stage('Test') {
      steps {
        sh 'npm test'
      }
    }
  }
}
Without a Shared Library, you’d copy and paste this snippet into every repository—leading to:
ProblemImpact
DuplicationHard to maintain multiple Jenkinsfiles
InconsistencyDifferent pipelines drift over time
ComplexityUpdates become error-prone
The image explains the benefits of using a shared library, highlighting issues like duplication, inconsistency, and complexity with corresponding icons.
By extracting common logic—like setup, notifications, or deployment—into a central repository, you get:
  • Better maintainability
  • Unified pipeline behavior
  • Easier on-boarding for new team members

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Example: Centralizing a Welcome Message

Imagine your DevOps team wants every pipeline to greet developers: 
pipeline {
  agent any
  stages {
    stage('Welcome') {
      steps {
        sh 'echo Welcome to the DevOps team from Dasher Organization'
      }
    }
    // ...
  }
}
When “Dasher” rebrands to “KodeKloud,” updating dozens of Jenkinsfiles is labor-intensive. Instead, create a welcome.groovy step in your Shared Library: 
// vars/welcome.groovy
def call() {
  sh 'echo Welcome to the DevOps team from KodeKloud Organization'
}
Then, load and invoke this function in your Jenkinsfile: 
@Library('kode-kloud-shared-library') _
pipeline {
  agent any
  stages {
    stage('Welcome') {
      steps {
        welcome()
      }
    }
    // ...
  }
}
Now, editing one file in the Shared Library updates every pipeline automatically.

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Setting Up a Shared Library in Jenkins

To configure a Shared Library:
  1. Create a Git repository dedicated to your shared steps and utilities.
  2. In Jenkins, go to Manage Jenkins → Configure System → Global Pipeline Libraries.
  3. Click Add and specify:
    • Name: A unique identifier (e.g., kode-kloud-shared-library)
    • Default Version: Branch or tag (e.g., main)
    • Retrieval Method: Modern SCM → Git URL
    • Advanced Options: Allow overriding the default version, load implicitly, etc.
Make sure Jenkins has read access to your Git repository. If you use credentials, add them under Manage Jenkins → Credentials.
The image outlines steps to set up a shared library in Jenkins, including repository setup, Jenkins configuration, and writing custom steps with Groovy functions.

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Repository Structure

A clear directory layout helps Jenkins locate your scripts: 
(root)
├── src
│   └── org
│       └── foo
│           └── Bar.groovy       # Optional: compiled Groovy classes
├── vars
│   ├── welcome.groovy            # Defines the 'welcome' pipeline step
│   └── welcome.txt               # Documentation for 'welcome'
└── resources
    └── org
        └── foo
            └── bar.json          # Optional: static resource files
DirectoryPurpose
src(Optional) Groovy/Java classes
varsRequired: global pipeline steps (camelCase)
resources(Optional) static files accessed via libraryResource
The image shows a diagram of a shared library repository structure, detailing directories and files for Groovy source files, global variables, and resource files. It includes folders like src, vars, and resources, with specific files such as Bar.groovy and bar.json.

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Configuring Global Pipeline Libraries

Once your repo is ready:
  1. Manage Jenkins → Configure System → Global Pipeline Libraries.
  2. Add Library with:
    • Name: kode-kloud-shared-library
    • Default Version: main
    • Load implicitly (optional)
    • SCM: Git URL and credentials
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 options like allowing the default version to be overridden and including library changes in job recent changes.

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Using Your Shared Library

In each Jenkinsfile, include the @Library annotation to load your shared code: 
@Library('kode-kloud-shared-library') _
pipeline {
  agent any
  stages {
    stage('Welcome') {
      steps {
        welcome()
      }
    }
    stage('Build') {
      steps {
        // your build steps...
      }
    }
  }
}
The welcome() step now references vars/welcome.groovy from your Shared Library, keeping pipelines concise and maintainable.

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