Introduction to Jenkins

Jenkins is an open-source automation server, and for a long time the default answer to "how do we run CI/CD here." It's free, endlessly extensible via plugins, and still runs the pipelines of a huge share of the software industry.

Controller and agents

Jenkins splits its work across two roles:

• The controller (historically called the "master") - the brain. It holds configuration, schedules work, and serves the web UI.
• Agents (historically "slaves") - the machines that actually run your builds. A controller can farm work out to dozens of agents, each with different tools installed (a Node agent, a Java agent, a GPU agent for ML builds, and so on).

This split matters because it lets Jenkins scale: the controller stays lightweight, and you add agents when you need more build capacity.

Jobs vs. Pipelines

Jenkins has two very different ways to define "what to run":

• A Freestyle job - a set of build steps configured by clicking through a web form. Quick to set up, hard to review or version.
• A Pipeline - the modern approach: the steps live in code (a Jenkinsfile), checked into your repository right alongside the application it builds.

Almost every team writing new automation today reaches for Pipelines - you'll build one in the next lesson.

Checking on a service

Jenkins itself typically runs as a background service, managed the same way any other long-running Linux service is - with systemctl:

systemctl status jenkins

A healthy Jenkins controller shows up as active (running), the exact same way nginx or any other daemon would.

When you're ready, hit Mark complete and move to the next lesson.