Jenkins
Also known as: Jenkins CI, Hudson, Jenkinsfile
Jenkins is an open-source automation server used to build, test, and deploy software.
It's the most widely deployed CI/CD tool in enterprises, valued for its flexibility and the thousands of plugins available for every imaginable integration. Unlike GitHub Actions or GitLab CI, Jenkins runs on infrastructure you manage.
Jenkins, explained at three levels
At home
Jenkins is a program you install on a server to automatically build and test your software. When code is pushed, Jenkins runs your build scripts, reports whether tests passed, and can deploy your app. It's like having a robot assistant that runs your checklists for you.
At work
Jenkins is the behind-the-scenes automation system in many software teams. It watches for code changes, runs tests, and deploys applications. It's self-hosted, giving teams full control over how and where builds run.
At home
Jenkins pipelines are defined in a Jenkinsfile (Groovy-based DSL) checked into the repository. Jenkins has thousands of plugins for integrations (GitHub, Jira, Docker, AWS, Slack). Build agents can run on the same server or be distributed across many machines. Jenkins is highly flexible but requires significant administration.
At work
Jenkins' declarative pipeline syntax defines stages and steps; scripted pipeline syntax provides full Groovy programming for complex logic. Shared Libraries let teams centralize common pipeline logic across projects. Jenkins X was a cloud-native extension for Kubernetes, though it has since been superseded by other tools.
At home
Jenkins' plugin architecture means stability depends on plugin quality and compatibility. Version updates risk breaking plugin combinations -- a common source of pain in Jenkins administration. The Jenkins Configuration as Code (JCasC) plugin addresses this by defining Jenkins configuration in YAML rather than through the GUI.
At work
Large Jenkins deployments use the Controller/Agent model: a central Jenkins controller delegates builds to many agents, possibly in Kubernetes pods (ephemeral agents via the Kubernetes plugin) that spin up per build and terminate when done. Artifact management via Nexus or Artifactory integrates with Jenkins for dependency caching and release artifact storage. Modern organizations sometimes maintain Jenkins alongside GitHub Actions -- Jenkins for complex legacy builds, Actions for new services.
Real-world examples
At home
Jerome's company has used Jenkins for 10 years and has hundreds of jobs configured. While new projects use GitHub Actions, the legacy monolith build still runs in Jenkins because migrating its 50-plugin pipeline would take months.
At work
Lena's team runs Jenkins on Kubernetes with ephemeral agents. Each build spins up a Docker-in-Docker pod, runs the pipeline (checkout, test, build image, push to registry), and terminates. No persistent build agents to maintain.
Common confusions
- Jenkins is outdated and should be replaced immediately — Jenkins remains a valid choice for complex, self-hosted CI needs. Its flexibility and plugin ecosystem handle scenarios that cloud CI tools struggle with. The 'replace Jenkins' decision depends on migration cost vs. benefit.
- Jenkins is free with no drawbacks — Jenkins itself is free, but it requires servers to run, engineering time to maintain, and ongoing plugin management. The total cost of ownership often exceeds paid cloud CI services for small teams.
For analysts
Jenkins can trigger data pipeline scripts on a schedule or on demand, integrating with databases, APIs, and reporting tools. Though more complex to set up than newer tools, its flexibility handles sophisticated multi-step workflows.
History & origin
Jenkins began as Hudson, created by Kohsuke Kawaguchi at Sun Microsystems in 2004. After Oracle acquired Sun and a dispute over the Hudson name, the community forked the project as Jenkins in 2011. Jenkins became the dominant CI/CD server for a decade, largely because it predated cloud-native alternatives and enterprises invested heavily in Jenkins infrastructure and plugins. Despite competition from GitHub Actions, GitLab CI, and CircleCI, Jenkins remains widely deployed in enterprises -- particularly those with complex, legacy build requirements.