Jenkins Shared library :

Jenkins Shared Libraries allow you to define reusable code, functions, and steps that can be shared across multiple pipelines. This promotes code reuse, consistency, and maintainability in your Jenkins pipelines. Here's an explanation of the concept with an example using a Declarative Pipeline :

1. Create the Shared Library :

1.1. In your version control system (e.g., Git), create a repository for your shared library code.

1.2. Inside the repository, create a vars directory. This is where you'll define your reusable pipeline steps.

1.3. In the vars directory, create a Groovy file (e.g., mySharedSteps.groovy) for your shared steps.

1.4. Define the shared steps in the Groovy file. For example, let's create a simple step that echoes a message:

// vars/mySharedSteps.groovy
def echoMessage(message) {
    echo "Shared Library says: ${message}"
}

2. Configure Jenkins to Use the Shared Library :

2.1. In Jenkins, go to "Manage Jenkins" > "Configure System."

2.2. Under the "Global Pipeline Libraries" section, add a new library:

• Name: Enter a name for your library (e.g., MySharedLibrary).

• Default version: Specify a branch or tag in your repository.

• Retrieval method: Choose "Modern SCM" and select your version control system (e.g., Git).

• Project repository: Enter the URL of your shared library repository.

2.3. Save the configuration.

3. Using the Shared Library in a Declarative Pipeline :

3.1. In your project's Jenkinsfile, you can now use the shared steps defined in your library :

@Library('MySharedLibrary') _
pipeline {
    agent any

    stages {
        stage('Use Shared Steps') {
            steps {
                script {
                    echoMessage("Hello from Shared Library!")
                }
            }
        }
    }
}

3.2. The @Library annotation imports and uses the shared library in your pipeline.

3.3. The echoMessage step is provided by the shared library and can be used directly in your pipeline.

4. Benefits of Shared Libraries :

• Code Reusability: You can define complex logic, common patterns, and custom steps in the shared library and use them across multiple pipelines.

• Consistency: Shared libraries ensure that the same logic is applied consistently across different pipelines.

• Maintainability: Updates and improvements made to the shared library are automatically reflected in all pipelines that use it.

• Versioning: You can control which version of the shared library is used in your pipelines by specifying the library version in your Jenkinsfile.

• Separation of Concerns: By centralizing common functionality in the library, your pipeline definitions become more focused on the specific tasks of your project.

Shared Libraries are a powerful way to extend the capabilities of your Jenkins pipelines and promote best practices and standardization across your organization's CI/CD processes.