Jenkins — The Original Open-Source Automation Server

What Jenkins Does

• Pipelines — Jenkinsfile (Groovy) declarative or scripted
• Freestyle jobs — GUI-configured legacy jobs
• Distributed builds — controller + agents on multiple machines
• Plugins — 2000+ for source control, build tools, deploy targets, notifications
• Multibranch — auto-discover branches and PRs
• Shared libraries — reusable Groovy libraries across pipelines
• Credentials store — encrypted secrets management
• Blue Ocean — modern pipeline UI
• CloudBees integrations — enterprise extensions

Architecture

Jenkins controller hosts the UI, scheduler, and job configuration. Agents (formerly slaves) execute builds in parallel, connected via JNLP, SSH, or Kubernetes pods. Pipelines are checkpointed — survive controller restarts.

Self-Hosting

# docker-compose.yml
version: "3"
services:
  jenkins:
    image: jenkins/jenkins:lts-jdk17
    ports: ["8080:8080", "50000:50000"]
    volumes:
      - jenkins-data:/var/jenkins_home
    environment:
      JAVA_OPTS: "-Djenkins.install.runSetupWizard=false"
volumes:
  jenkins-data:

Key Features

• Pipeline-as-code (Jenkinsfile)
• 2000+ plugins
• Distributed builds
• Matrix builds
• Shared libraries
• Credentials store
• Email/Slack/Teams notifications
• Multi-branch pipelines
• Auto-scaling agents on Kubernetes
• LDAP, SAML, OAuth auth

Comparison

FAQ

Q: Is Jenkins outdated? A: It has lost many new projects to GitHub Actions and GitLab CI. But Jenkins is still the top choice in enterprises (especially where legacy pipelines and strict compliance matter). Its 2000+ plugins are unmatched.

Q: Compared to GitHub Actions? A: Actions are cloud-native, YAML is concise, and it deeply integrates with GitHub; Jenkins is self-hosted, Groovy is flexible, and its plugin ecosystem is unbeatable. The choice depends on hosting preference and integration needs.

Q: Performance and memory? A: It's a Java application; the controller typically needs at least 2GB of heap. Large-scale deployments (millions of jobs) require tuning the JVM and storage.

Sources

• Docs: https://www.jenkins.io/doc
• GitHub: https://github.com/jenkinsci/jenkins
• License: MIT