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In this lesson, you’ll learn how to leverage the Jenkins Configuration as Code (JCasC) plugin to define pipeline jobs, manage global settings, and install build tools—all through YAML. We’ll explore official demos, customize configurations, and apply them in your Jenkins instance.

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Prerequisites

  • Jenkins with Configuration as Code plugin installed
  • Access to Jenkins controller shell
  • Basic familiarity with YAML and Jenkins plugins

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1. Explore Example Configurations

The JCasC plugin demos on GitHub contain ready-made use cases:
You can browse the demos directory for examples ranging from security setups to cloud integrations.

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2. Configure Global Authorization

To set up a matrix-based authorization strategy, add the following to your jenkins-casc.yaml: 
jenkins:
  authorizationStrategy:
    globalMatrix:
      permissions:
        - "USER:Overall/Read:anonymous"
        - "GROUP:Overall/Administer:authenticated"
        - "USER:Overall/Administer:admin"

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3. Configure a Kubernetes Cloud

Click Config YAML under the Kubernetes demo to copy this snippet: 
unclassified:
  location:
    url: http://jenkins/

jenkins:
  clouds:
    - kubernetes:
        name: "advanced-k8s-config"
        serverUrl: "https://advanced-k8s-config:443"
        serverCertificate: "serverCertificate"
        skipTlsVerify: true
        credentialsId: "advanced-k8s-credentials"
        namespace: "default"
        jenkinsUrl: "http://jenkins/"
        jenkinsTunnel: "JenkinsTunnel"
        containerCapStr: 42
        maxRequestsPerHostStr: 64
        retentionTimeout: 5
        connectTimeout: 10
The image shows a GitHub repository page for a project related to configuring a Kubernetes plugin, with a list of files and a README section providing instructions.

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4. Install Build Tools

You can also install Node.js, Git, Maven, and SonarQube Scanner using JCasC. Here’s an example for Node.js: 
tool:
  nodejs:
    installations:
      - name: "NodeJS Latest"
        home: ""  # required until nodejs-1.3.4 release (JENKINS-57508)
        properties:
          installSource:
            installers:
              - nodeJSInstaller:
                  id: "12.11.1"
                  npmPackagesRefreshHours: 48  # default is 72

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Tool Installation Summary

ToolVersion IdentifierNotes
Node.js12.11.1Auto-installed; refreshes npm packages every 48 hours
GitDefaultUses system git binary
Maven3.9.8Managed via internal installer
SonarQube Scanner6.10Installed through the SonarRunner installer

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5. Edit Your jenkins-casc.yaml

On the controller, open or create your configuration file: 
cd /var/lib/jenkins/JENKINS_BACKUP
vi jenkins-casc.yaml
A comprehensive file may include credentials, SCM settings, tool definitions, and more: 
credentials:
  system:
    domainCredentials:
      - usernamePassword:
          description: 'Gitea Server Credentials'
          id: gitea-server-creds
          username: gitea-admin
          password: '{AQAAB...}'
          scope: GLOBAL
      - usernamePassword:
          description: 'Credentials for MongoDB'
          id: mongo-db-credentials
          username: superuser
          password: '{AQAAB...}'
          scope: GLOBAL
      - string:
          description: 'Mongo Database Username'
          id: moneo-db-username

git:
  installations:
    - home: "git"
      name: "Default"

maven:
  installations:
    - name: "M398"
      properties:
        - installSource:
            installers:
              - maven:
                  id: "3.9.8"

sonarRunnerInstallation:
  installations:
    - name: "sonarqube-scanner-610"
      properties:
        - installSource:
            installers:
              - sonarRunnerInstaller: {}

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6. Define Pipeline Jobs with Job DSL

In the demos folder, there’s a sample that uses the Job DSL plugin to create a folder and pipeline job:
The image shows a GitHub repository page for a Jenkins configuration-as-code plugin, displaying a list of YAML files and a README section about configuring seed jobs.
Add these job definitions to your jenkins-casc.yaml: 
jobs:
  - script: >
      folder('test-jobs')
  - script: >
      pipelineJob('test-jobs/default-agent') {
        definition {
          cps {
            script("""
              pipeline {
                agent any
                stages {
                  stage('test') {
                    steps {
                      echo 'hello'
                    }
                  }
                }
              }
            """.stripIndent())
          }
        }
      }

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7. Reload Configuration and Troubleshoot

After saving, go to Manage Jenkins → Configuration as Code → Reload Existing Configuration. You may see:
The image shows a Jenkins configuration page with a warning about a missing configurator for root elements. There are options to apply a new configuration, reload, download, and view the configuration.
If you encounter UnknownConfiguratorException: No configurator for the following root elements: jobs, it means the Job DSL plugin is not installed.
To resolve:
  1. Manage Jenkins → Manage Plugins
  2. Search for Job DSL and install.
  3. Reload or reapply your JCasC configuration.

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8. Verify Jobs and Tools

Once the DSL plugin is active, Jenkins will create the test-jobs folder and the default-agent pipeline automatically. You can also confirm tool installations under Manage Jenkins → Global Tool Configuration: 
pipeline {
  agent any
  stages {
    stage('test') {
      steps {
        echo "Hello"
      }
    }
  }
}
The image shows a Jenkins configuration interface with dropdown menus for managing system settings, plugins, and security options. The user is navigating through the "Manage Jenkins" menu.

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References

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