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Managing Jenkins through dozens of UI screens can be tedious. With the Configuration as Code (CasC) plugin, you define your entire Jenkins setup—including core settings, security, plugins, tools, and credentials—as YAML. In this guide, you’ll learn how to:
  • Install and enable the CasC plugin
  • Inspect your live Jenkins configuration
  • Modify a setting declaratively and apply it
  • Validate and reload configurations

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1. Installing the Configuration as Code Plugin

  1. In Jenkins, go to Manage Jenkins → Manage Plugins → Available.
  2. Search for Configuration as Code, select it, and click Install (restart if prompted).
The image shows the Jenkins plugin management interface, specifically the "Available plugins" section, with a search for "configuration as" displaying related plugins.
After restart, you’ll see Configuration as Code under Manage Jenkins → System Configuration.

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2. Exploring the Current Configuration

Navigate to Manage Jenkins → Configuration as Code. Here you can:
  • View Configuration: Download the live settings as YAML or JSON
  • Replace Configuration: Point to a file on disk or a Git repo
  • Reload: Reapply the last loaded settings
The image shows a Jenkins "Configuration as Code" interface, where users can replace configuration sources and perform actions like reloading, downloading, or viewing configurations.

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2.1 Downloaded Configuration Example

When you download your live settings, Jenkins outputs JSON or YAML. Below is a shortened JSON excerpt: 
{
  "jenkins": {
    "systemMessage": "Jenkins is ready to use.",
    "numExecutors": 5,
    "mode": "EXCLUSIVE",
    "scm": { "gitHub": "global-git-hub" },
    "credentials": [
      {
        "scope": "GLOBAL",
        "id": "gh_repo_secret_token",
        "username": "GitHub Username",
        "password": "GitHub Token"
      }
    ]
  }
}
CasC automatically converts JSON into YAML. A typical YAML will include sections like: 
jenkins:
  systemMessage: "Jenkins is ready to use."
  numExecutors: 5
  mode: "EXCLUSIVE"
security:
  apiToken:
    tokenGenerationOnCreationEnabled: false
unclassified:
  auditTrail:
    displayName: true
tools:
  maven:
    installations:
      - name: "M308"
        properties:
          - installSource:
              installers:
                - maven:
                    id: "3.9.8"
  nodejs:
    installations:
      - name: "nodejs-22-6-0"
        properties:
          - installSource:
              installers:
                - nodeJSInstaller:
                    id: "22.6.0"

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2.2 YAML Section Reference

SectionDescriptionExample Fields
jenkinsCore Jenkins settingssystemMessage, numExecutors, mode
securitySecurity and API token managementapiToken.tokenGenerationOnCreationEnabled
unclassifiedPlugin-specific configurationsauditTrail, slackNotifier
toolsTool installers (Git, Maven, Node.js)maven.installations, nodejs.installations
credentialsCredentials domains and secretsusernamePassword, string

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2.3 Credentials Example

credentials:
  system:
    domainCredentials:
      - credentials:
          - usernamePassword:
              id: "gitea-server-creds"
              description: "Gitea Server Credentials"
              username: "gitea-admin"
              password: "{AAABAAAAQ4e7IwFYLRu0yZlNsLqahKkpJFtDGTyKUsxQCU=}"
              scope: GLOBAL
          - string:
              id: "sonar-qube-token"
              description: "SonarQube Server Token"
              secret: "{AAABAAAAQpXMpOkYc2h9v0KshvCkdK8c9207YLPcYZ3ot64=}"
              scope: GLOBAL
You can explore more sections like global security, authorization strategies, and plugin settings by scrolling through the full YAML.

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3. Modifying Configuration via CasC

Let’s update the Jenkins system message. First, back up and edit your YAML on the controller: 
cd /var/lib/jenkins/JENKINS_BACKUP
cp /var/lib/jenkins/casc.yaml jenkins-casc.yaml.bak
vi jenkins-casc.yaml
Add or update the remotingSecurity block: 
remotingSecurity:
  enabled: true
  slaveAgentPort: 0
  systemMessage: "Loading data from Jenkins Configuration as Code"
Then, on Manage Jenkins → Configuration as Code, use Replace Configuration to point to: 
/var/lib/jenkins/JENKINS_BACKUP/jenkins-casc.yaml
Click Apply New Configuration. Jenkins will validate and apply the YAML, displaying a load timestamp.
Always back up your YAML and test in a non-production instance before applying major changes.

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4. Applying and Reloading Configuration

On the CasC page you can also:
  • Reload Existing Configuration: Reapply last known-good settings
  • Download Current Configuration: Fetch live YAML/JSON
  • View Documentation: Open [JCasC docs][casc-doc]
  • View JSON Schema: Inspect the schema for valid YAML
Here’s a snippet of the JCasC JSON schema: 
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "description": "Jenkins Configuration as Code",
  "type": "object",
  "properties": {
    "security": {
      "type": "object",
      "properties": {
        "apiToken": { "type": "object" }
      }
    },
    "cps": {
      "type": "object",
      "properties": {
        "hideSandbox": { "type": "boolean" }
      }
    }
  }
}
The image shows a Jenkins configuration page with options to apply a new configuration, reload, download, or view the existing configuration. It also includes a warning about the export not being directly usable for Jenkins YAML configuration.
For more details, see the [official CasC documentation][casc-doc] and explore the [Jenkins schema reference][casc-schema].

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