Why CI/CD before Jenkins?
Before you touch Jenkins, you need to understand the problem it solves: CI/CD.
Continuous Integration (CI)
CI is the practice of automatically integrating code changes from multiple contributors into a shared repository several times a day. Every push triggers an automated build and test cycle.
Why does this matter?
Imagine you and three other developers are working on the same codebase. Without CI, everyone works in isolation for a week, then tries to merge everything on Friday. That Friday becomes a nightmare — conflicts everywhere, tests failing, nobody knows whose change broke what.
CI solves this by integrating and testing continuously, catching problems the moment they are introduced.
Goal: Catch bugs early, before they reach production.
CI flow:
Developer pushes code
↓
Jenkins detects the push (via webhook or poll)
↓
Jenkins pulls the latest code
↓
Runs automated tests
↓
Reports: Pass or Fail
Continuous Delivery (CD)
CD extends CI by automatically packaging your app and getting it ready for deployment. After every passing build, you have a deployable artifact — a Docker image, a JAR, a ZIP — ready to go live at any time.
Continuous Deployment
One step further — every change that passes all automated tests is automatically deployed to production with zero manual intervention.
| Stage | What happens | Manual step? |
|---|---|---|
| CI | Build + Test | None |
| Continuous Delivery | Build + Test + Package | Deployment approval |
| Continuous Deployment | Build + Test + Package + Deploy | None |
Continuous Delivery and Continuous Deployment sound the same. The difference is one thing — in Delivery, a human still approves the final deploy. In Deployment, even that step is automated.
Real-world CI/CD flow
By Day 4 you will have built this end-to-end:
Developer
↓
GitHub
↓
Webhook
↓
Jenkins
↓
Build → Test → Docker Build → Docker Hub → Deploy → Notification
Day 1 starts smaller: install Jenkins and run a Freestyle job that clones GitHub and runs a shell script. Each day adds a layer until you reach Multibranch + Master–Agent.