Jenkins Pipeline Guide

What You Will Learn

Jenkins automates build, test, and deployment workflows. This guide explains pipelines, agents, stages, credentials, artifacts, and deployment flow.

Prerequisites

• Git basics
• One Java or React project
• Basic CI/CD understanding

Concept Overview

A Jenkins pipeline is usually defined in a Jenkinsfile. It describes what Jenkins should do when code changes: checkout, install dependencies, run tests, build artifacts, create images, and deploy.

Step-by-Step Explanation

1. Connect Jenkins to your Git repository.
2. Create a Jenkinsfile.
3. Define an agent.
4. Add stages for checkout, build, test, package, and deploy.
5. Store secrets in Jenkins credentials.
6. Archive artifacts if needed.
7. Add notifications for failed builds.

Code Example

pipeline {
  agent any

  stages {
    stage('Install') {
      steps { sh 'npm ci' }
    }
    stage('Test') {
      steps { sh 'npm test -- --watch=false' }
    }
    stage('Build') {
      steps { sh 'npm run build' }
    }
  }
}

Real-World Use Cases

• Building Spring Boot JAR files
• Running frontend lint and build checks
• Creating Docker images
• Pushing images to a registry
• Deploying to EC2, ECS, or Kubernetes

Best Practices

• Keep pipelines readable.
• Store credentials securely.
• Fail fast when tests or lint fail.
• Use separate stages for visibility.
• Avoid hardcoding environment-specific values.
• Keep deployment approval manual for production when needed.

Common Mistakes

• Putting secrets in the Jenkinsfile
• Running all commands in one large stage
• Ignoring failed tests
• Not cleaning workspaces
• Deploying to production from any branch

Interview Questions

• What is a Jenkinsfile?
• What is the difference between declarative and scripted pipeline?
• How do Jenkins credentials work?
• Why split a pipeline into stages?
• How can Jenkins deploy Dockerized applications?

Summary

Jenkins pipelines make delivery repeatable. Clear stages, secure credentials, and branch-based deployment rules are the foundation of reliable CI/CD.