Introduction to CI/CD

Why CI/CD?

For continuous integration and continuous deployment, Jenkins is the most widely used tool in the DevOps world. It automates the way code moves from a developer's laptop to a live production server.

CI — Continuous Integration

CI is the combination of continuous build + continuous test. Whenever a developer commits code using a source code management tool like GIT, the CI pipeline automatically picks up the change, builds it, and runs unit tests.

• Since new code is integrated with old code immediately, we quickly know if the code is a success or failure.
• Errors are found much faster than manual testing.
• Products get delivered to the client more frequently.
• Developers don't need to perform manual build/test tasks.
• Overall it reduces developer effort by roughly 20% to 30%.

CI Server

On a CI Server, Build, Test & Deploy activities are all performed together on a single server.

CI Server = Build + Test + Deploy

CD — Continuous Delivery / Deployment

Continuous Delivery

Continuous Delivery makes a build artifact available for deployment. Whenever a new build artifact is ready, it is automatically placed in the desired environment. Deploying to production is still a manual step here — it needs human approval.

Continuous Deployment

• Every commit is automatically tested, built, and deployed straight to the production server.
• No manual approval is required.
• Deployment to production is fully automatic.
• In practice, around 99% of companies don't fully adopt this because of the risk involved.

The CI/CD Pipeline

The overall flow looks like a mini Software Development Life Cycle (SDLC) with 6 phases:

1. Version Control — Developers commit code using GIT or SVN.
2. Build — The code gets compiled (e.g. using Maven for Java).
3. Unit Test — Code-level testing using tools like SonarQube / mvn test.
4. Deploy — Code is deployed to a Dev/Testing (pre-prod) environment.
5. Auto Test — Application-level automation testing using Selenium/JUnit.
6. Deploy to Production — If everything looks good, the code goes live.

If an error occurs at any stage, feedback is given immediately and the issue is fixed before moving forward — this is what makes the entire SDLC automatic and fast when using Jenkins.