Jenkins CI CD Basics
Every software team writes code, tests it, packages it, and delivers it to users. Doing these jobs by hand wastes hours and invites mistakes. Continuous Integration and Continuous Delivery, known as CI/CD, turn those manual jobs into an automatic routine. Jenkins runs that routine for you.
The Layman's View
Picture a group of friends baking one big cake. Each friend adds an ingredient at a different time. If nobody tastes the batter until the end, a wrong ingredient ruins the whole cake. Now imagine a helper who tastes the batter after every single addition and shouts the moment something tastes wrong. That helper is Continuous Integration. The cake is your software, and Jenkins is the helper.
Continuous Integration
Continuous Integration means developers merge their code into a shared repository many times a day. Each merge triggers an automatic build and an automatic test run. The team learns about a broken change within minutes instead of days.
What CI Gives a Team
- Small changes reach the shared code often, so conflicts stay small.
- Automatic tests catch bugs while the author still remembers the change.
- Everyone trusts that the main branch always builds.
Continuous Delivery and Continuous Deployment
Continuous Delivery extends CI. After the tests pass, the pipeline prepares a release package and moves it to a staging area. A person presses a button to send it to users. Continuous Deployment removes that button. Every change that passes all checks goes live automatically.
| Practice | Ends At | Human Approval |
|---|---|---|
| Continuous Integration | Build and test | Not needed |
| Continuous Delivery | Release-ready package | Needed before production |
| Continuous Deployment | Live in production | Not needed |
The Flow of a CI/CD Pipeline
Developer
|
| pushes code
v
+-------------+ +-----------+ +-----------+
| Git Server |-->--| Jenkins |-->--| Build |
+-------------+ +-----------+ +-----------+
|
v
+-------------+ +-----------+ +-----------+
| Production |--<--| Staging |--<--| Test |
+-------------+ +-----------+ +-----------+
Read the diagram as a conveyor belt. Code enters on the left, passes each station, and leaves at production. A failure at any station stops the belt and alerts the team.
Where Jenkins Fits
Jenkins acts as the conductor of the pipeline. It watches the repository, starts the build, runs the tests, collects the results, and triggers the deployment. Jenkins does not write code or tests. It coordinates the tools that do.
Tools Jenkins Coordinates
| Task | Common Tool |
|---|---|
| Source control | Git, GitHub, GitLab |
| Build | Maven, Gradle, npm |
| Testing | JUnit, Selenium, pytest |
| Packaging | Docker |
| Deployment | Kubernetes, SSH scripts |
A Day Without CI/CD and a Day With It
Without CI/CD
A developer finishes a feature on Friday. A teammate merges it by hand on Monday. The build fails because two features clash. The team spends Tuesday hunting for the cause. The release slips by a week.
With CI/CD
A developer pushes a feature on Friday. Jenkins builds it within seconds and reports a failing test. The developer fixes the test in ten minutes. The release stays on schedule.
Key Terms to Remember
Build
A build turns source code into a runnable program or package.
Pipeline
A pipeline lists the stages that code travels through, from commit to release.
Artifact
An artifact is a file that a build produces, such as a JAR file or a Docker image.
Trigger
A trigger is an event that starts a pipeline, such as a code push or a daily timer.
Feedback Loop
A feedback loop is the time between a code change and the result of its tests. Short loops make teams faster.
Habits That Make CI/CD Work
- Commit small changes often.
- Keep the build fast, ideally under ten minutes.
- Fix a broken build before starting new work.
- Store every setting and script in version control.
- Write automatic tests for every important feature.
Teams that follow these habits release more often and with fewer surprises. Jenkins supplies the engine, and these habits supply the direction.