Note_Tech

All technological notes.

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Jenkins - Fundamental

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• Jenkins - Fundamental
  • Fundamental
    • Items
    • Build
  • Architecture
  • Core Components
    • Jenkins Controller (Master)
    • Jenkins Agents (Workers)
    • How It Works (Execution Flow)
    • Common Deployment Patterns
    • Plugins
  • Common Configurations
    • Environment Variables
    • Jenkins URL
    • Notification
  • Common Practices
    • Blue-Green deployment strategy
    • Backup

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Fundamental

• default path:
  • Windows: C:\Program Files (x86)\Jenkins\
  • Linux: /var/lib/jenkins
• Restart:
  • manually on control panel
  • cli: sudo systemctl restart jenkins
• Default Port Number: 8080
• Jenkins Build Executor:
  • a processing slot on a build agent (or controller) that runs a single concurrent build task, effectively acting as a worker thread.
• Jenkins Pipeline as Code
  • the practice of defining a project’s entire build, test, and deployment process through code rather than manual configuration in the Jenkins web UI.

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Items

Items	Description
Pipeline	A continuous delivery pipeline, which is configured via a Jenkinsfile (Pipeline as Code).
Freestyle Project	General-purpose job type.
Folder	A container that stores nested items
Multibranch Pipeline	managing CI/CD pipelines for multiple branches in one version control repository.
Organization Folders	Creates a set of multibranch project subfolders by scanning for repositories.

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Build

• build
  • a single execution instance of a Jenkins job or project.

Jenkins build lifecycle:

1. Triggering a Build:
   • Initiating the build process through manual, scheduled, or event-driven triggers.
2. Initialization:
   • Setting up the build environment and resources.
3. Source Code Checkout:
   • Getting the latest code from version control.
4. Build Process:
   • Executing build scripts, compiling code, and performing necessary tasks.
5. Testing:
   • Running test suites and reporting results.
6. Deployment:
   • Releasing built artifacts to target environments.
7. Post-Build Actions:
   • Archiving artifacts, publishing reports, and sending notifications.
8. Recording and Reporting:
   • Collecting and storing build data and results.
9. Clean-Up:
   • Managing resources and resetting the environment.

• Notifications: Keeping stakeholders informed of build status.
• Artifact Storage: Storing generated artifacts for future use.
• Logging and Auditing: Maintaining detailed logs for auditing and troubleshooting.
• Post-Build Analysis and Continuous Improvement: Analyzing build results for process enhancement.

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Architecture

• a controller–agent (master–worker) architecture

        +----------------------+
        |     Jenkins UI       |
        |  (Web Interface/API) |
        +----------+-----------+
                   |
                   v
        +----------------------+
        |   Jenkins Controller |
        |  (Master Node)       |
        +----------+-----------+
                   |
        ----------------------------
        |            |            |
        v            v            v
+-------------+ +-------------+ +-------------+
|   Agent 1   | |   Agent 2   | |   Agent N   |
| (Worker)    | | (Worker)    | | (Worker)    |
+-------------+ +-------------+ +-------------+

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Core Components

Jenkins Controller (Master)

• Jenkins Controller
  • the central controlling serve
• Responsibilities:
  • Manage jobs and pipelines
  • Schedule builds
  • Assign tasks to agents
  • Store configuration and build history
• Provides:
  • Web UI
  • REST API
  • Authentication & authorization
• Controller does not run heavy workloads
• Agents handle:
  • Compilation
  • Testing
  • Deployment

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• Jenkins jobs
  • the runnable, configurable projects or tasks within the Jenkins automation server that automate software development workflows, such as building, testing, and deploying applications.
• Jenkins Pipeline

  • automated process that describes your entire software delivery workflow (Build, Test, Deploy).

  • Types:

    • Pipeline (Jenkinsfile) (recommended)
    • Freestyle jobs (basic UI-driven)
      • Written in Groovy-based DSL
      • Supports CI/CD workflows
• Queue
  • a temporary waiting area for scheduled build jobs that are pending execution due to a lack of available executors (nodes).
  • Controller schedules jobs based on:
    • Available executors
    • Node labels
    • Resource constraints
• Plugins
  • a software extension that adds specific features or integrations to the core Jenkins environment
  • Common plugins:
    • Git / GitHub integration
    • Docker
    • Kubernetes
    • AWS
    • Pipeline plugins

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Jenkins Agents (Workers)

• Jenkins Agents

  • the machines, containers, or cloud instances that connect to the Jenkins Controller to execute build jobs and pipelines.

  • Types:

    • Static agents (pre-configured)
    • Dynamic agents (provisioned on demand, e.g., Kubernetes)

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• Executor
  • a dedicated slot on a build agent (or controller) that executes a single build job or pipeline stage at a time.
  • acts as a thread within an agent, meaning the number of executors per node determines how many jobs can run concurrently.
  • Example:
    • 1 agent with 4 executors → can run 4 jobs concurrently
• Workspace
  • a disposable directory on the file system of a Jenkins Node where a specific job or Pipeline executes its work.
  • It serves as a temporary “sandbox” for checking out source code, compiling files, and running tests.
  • Stores:
    • Source code
    • Build artifacts
    • Temporary files

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How It Works (Execution Flow)

1. Developer pushes code to GitHub
2. Jenkins detects change (webhook or polling)
3. Job is triggered and placed in queue
4. Controller selects an available agent
5. Agent executes pipeline steps
6. Results are sent back to controller
7. Output shown in Jenkins UI

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Common Deployment Patterns

1. Single Node (Small Setup) Controller + executor on same machine Simple but not scalable
2. Controller + Multiple Agents (Recommended) Production-ready setup
3. Cloud-Native Jenkins Controller in VM/container Agents dynamically provisioned (Kubernetes)

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Plugins

• Jenkins plugins
  • add-on modules that extend the functionality of the core Jenkins automation server, allowing it to integrate with thousands of tools for CI/CD, source control (Git), cloud platforms (Docker, Kubernetes), and build tools (Maven).
• Common plugins:
  • Pipeline: Stage ViewVersion

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Common Configurations

Environment Variables

• Built-in global variable env
  • ref: https://www.jenkins.io/doc/book/pipeline/jenkinsfile/#using-environment-variables
• Custome global env var
  • Manage Jenkins > System > Global properties > check Environment variables
• Pipeline env var

pipeline {
    agent {
        label '!windows'
    }

    environment {
        DISABLE_AUTH = 'true'
        DB_ENGINE    = 'sqlite'
    }

    stages {
        stage('Build') {
            steps {
                echo "Database engine is ${DB_ENGINE}"
                echo "DISABLE_AUTH is ${DISABLE_AUTH}"
                sh 'printenv'
            }
        }
    }
}

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Jenkins URL

• Manage Jenkins > System > Jenkins Location
  • Jenkins URL:

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Notification

• Email
  • Plugin: Email Extension Plugin

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Common Practices

Blue-Green deployment strategy

• Implementing a Blue-Green deployment in Jenkins involves:
  • Setting up two identical environments: blue and green.
  • Deploying the new version to the green environment.
  • Testing in the green environment.
  • Switching traffic to green if testing succeeds.
  • Monitoring and potential rollback if issues arise.
• Key benefits:
  • zero downtime,
  • quick rollback,
  • reduced risk,
  • safe testing,
  • continuous delivery, scalability, enhanced monitoring, and improved confidence in deploying changes.

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Backup

• Backup JENKINS_HOME directory
• Use ThinBackup plugin
• Use Backup plugin
• Version control job configurations