Jenkins Configuration as Code JCasC

Before exploring Jenkins Configuration as Code, let’s revisit Infrastructure as Code (IaC). As organizations scale, managing infrastructure manually becomes error-prone and inefficient. Tools like Ansible, Terraform, Puppet, and Chef let you define network, compute, storage, and security resources as code—making deployments repeatable, versioned, and automated.

The image illustrates "Infrastructure as Code" with icons for templates, scripts, and policies, and features tools like Ansible, Terraform, Chef, and Puppet. It also highlights areas such as network, application, storage, security, and cloud infrastructure.

Just as IaC revolutionizes infrastructure management, Jenkins Configuration as Code (JCasC) brings the same benefits to your CI/CD platform.

Managing Jenkins as Code

You can manage Jenkins configurations in three domains:

Infrastructure: agents, nodes, cloud integrations
Jobs: build steps, triggers, and post-build actions
System: global security, credentials, plugins, and tools

Choose from these methods:

Method	Use Case	Reference
CLI	Quick, ad-hoc server management	Jenkins CLI
REST API	Programmatic integration with external tools	Remote Access API
Client Libraries	Custom scripts in Java, Python, or Go
IaC Tools	Provision Jenkins master and agents	Ansible, Terraform, Chef
Containerization (Docker)	Portable, consistent Jenkins environments	Docker Hub

The image is a diagram titled "Managing Jenkins as Code," highlighting five components: Command-Line Tools, RESTful API, Client Libraries, Infrastructure as Code (IaC) Tools, and Containerization. It categorizes these under "Jenkins Infrastructure" with other sections for "Jenkins Job Configurations" and "Jenkins System Configurations."

Code-Based Job Configuration

Managing jobs through the UI works for a few pipelines, but at scale you’ll want version-controlled definitions:

Plugin / Feature	Description	Link
Job DSL Plugin	Define jobs in Groovy, mirroring UI settings in code	Job DSL
Job Builder Plugin	Describe jobs using YAML or JSON	Jenkins Job Builder
Jenkins Pipeline	Script complex workflows in a `Jenkinsfile`	Pipeline
Multibranch Pipeline	Auto-create pipelines by scanning SCM branches	Multibranch Pipeline

The image is a diagram titled "Managing Jenkins as Code," showing different components like Jenkins Infrastructure, Job Configurations, and System Configurations, with tools such as JobDSL plugin, Job builder plugin, Jenkins Pipeline, and Multibranch.

These approaches ensure your CI jobs are reusable, maintainable, and easily audited through Git history.

System Configuration Challenges

Manually configuring credentials, plugins, tools, and security via the UI presents:

Time-consuming menus and clicks
Risk of inconsistent settings across environments
Higher chance of human error

Warning

Avoid manual system tweaks in production. Misaligned configurations can break pipelines and introduce security gaps.

The image is a presentation slide about managing Jenkins as code, highlighting Jenkins infrastructure, job configurations, and system configurations, with a focus on system configuration details and challenges like being time-consuming, error-prone, and inefficient.

Groovy Init Scripts

Historically, many admins scripted Jenkins setup with Apache Groovy init scripts. While powerful, these scripts require deep knowledge of the Jenkins API and plugin internals.

The image is about managing Jenkins as code, highlighting Jenkins infrastructure, job configurations, and system configurations, with a focus on Groovy scripting and Jenkins internals.

Introducing Jenkins Configuration as Code

The Configuration as Code plugin enables you to define your entire Jenkins instance in a single human-readable YAML file. This mirrors every option in the UI:

Version-controlled in Git alongside your apps
Self-configuring new instances for zero-touch provisioning
Fewer manual errors—YAML syntax is easy to validate

The image features a cartoon character holding a wrench next to text about "Jenkins Configuration as Code (JCasC)" highlighting benefits like version control integration, repeatable deployments, and reduced errors.

Getting Started

Install Configuration as Code from Manage Jenkins → Plugins.
Navigate to Manage Jenkins → Configuration as Code → View Configuration.
Jenkins exports your current setup as jenkins.yaml.

jenkins:
  numExecutors: 2
  mode: NORMAL
  agentProtocols:
    - "JNLP4-connect"
    - "Ping"
  crumbIssuer:
    standard:
      disableRememberMe: false
  globalNodeProperties:
    - envVars:
        - key: "TEST_VAR"
          value: "example_value"

Commit jenkins.yaml to your repo. Future Jenkins startups will apply this file automatically.

The image illustrates Jenkins Configuration as Code (JCasC) with a YAML file structure and a cartoon character holding a wrench. It includes sections for system settings, nodes, and cloud configurations.

Customizing Your YAML

jenkins: Global settings (system message, executors)
tools: Define JDKs, Maven, Gradle installations
credentials: Mirror entries under Manage Jenkins → Credentials
unclassified: Miscellaneous plugin-specific settings
views: Configure custom list or pipeline views

Example—adding a welcome message, a Maven tool, and list views:

jenkins:
  systemMessage: "Welcome to the DevOps revolution!"
tools:
  maven:
    installations:
      - name: "maven-3.8.0"
        home: "/usr/share/maven"
views:
  list:
    - name: "All Jobs"
      filter: ".*"
    - name: "Active Jobs"
      filter: "status != COMPLETED"

Apply changes immediately via Manage Jenkins → Configuration as Code—no restart required.

Links and References

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