Jenkins
What is it?
Jenkins is an open-source automation server that builds, tests, and deploys software through configurable pipelines you host yourself.
Explain like I'm 5
Why was it created?
It was created to automate building and testing software so teams could integrate changes continuously instead of by hand.
Where is it used?
- Continuous integration pipelines
- Automated builds and tests
- Deployments
- Self-hosted CI/CD environments
Why should developers care?
Jenkins is a long-established CI/CD tool still widely used in many companies, so you may inherit or maintain Jenkins pipelines.
How does it work?
Jenkins runs on a server you manage. You define pipelines (often as code) describing build, test, and deploy stages; Jenkins executes them on agents, triggered by code changes or schedules, with results in a dashboard.
Real-world example
A company runs Jenkins on its own servers to build its app, run tests, and deploy to internal environments on every merge.
Common use cases
- Self-hosted CI/CD
- Complex custom pipelines
- Integrating many tools via plugins
- Automated builds and deployments
Advantages
- Free and open-source
- Huge plugin ecosystem
- Highly customizable
- Full control via self-hosting
Disadvantages
- You must host and maintain it
- Plugin sprawl can cause issues
- Setup and upkeep effort
- Dated UX compared to newer tools
When should you use it?
When you want full control of a self-hosted, highly customizable CI/CD server.
When should you avoid it?
When a managed service like GitHub Actions removes maintenance burden you don't want.
Alternatives
Related terms
Interview questions
Beginner
- What is Jenkins used for?
- What is a build pipeline?
Intermediate
- What is a Jenkins agent?
- What is pipeline-as-code?
Senior
- What are the trade-offs of self-hosted Jenkins vs managed CI?
- How do you keep a Jenkins setup maintainable?
Common misconceptions
- "Jenkins is outdated and unused" — it's older but still widely deployed in many organizations.
- "Jenkins is fully managed" — you're responsible for hosting, upgrades, and plugins.
Fun facts
- Jenkins began as a project called Hudson before being renamed.
- Pipelines can be defined as code in a Jenkinsfile checked into your repo.
Timeline
- 2011 — Renamed to Jenkins from Hudson
Learning resources
Quick summary
Jenkins is a self-hosted, highly customizable automation server for building, testing, and deploying software via pipelines.
Cheat sheet
- Self-hosted CI/CD server
- Pipelines, often as code
- Huge plugin ecosystem
- You manage hosting and upkeep