Build Your First CI/CD Pipeline with Jenkins: Complete Guide

CI/CD stands for Continuous Integration / Continuous Delivery (or Deployment). It automates the process of building, testing, and deploying code changes — reducing human error and speeding up releases.

Continuous Integration: Every code commit triggers automated builds and tests. Developers merge code to a shared branch frequently (multiple times a day), catching bugs early.

Continuous Delivery: After CI, code is automatically deployed to a staging environment. Continuous Deployment goes further — every passing build is automatically deployed to production.

Benefits: 10x faster release cycles, 90% fewer production bugs, instant rollback capability, and consistent deployments. Companies using CI/CD deploy hundreds of times per day (Netflix, Amazon).

Jenkins is the most popular open-source CI/CD tool with 1,800+ plugins. Install on Ubuntu: sudo apt update && sudo apt install openjdk-17-jre -y (Jenkins needs Java).

Add Jenkins repository: curl -fsSL https://pkg.jenkins.io/debian/jenkins.io-2023.key | sudo tee /usr/share/keyrings/jenkins-keyring.asc, then add the repo and install with apt.

Start Jenkins: sudo systemctl start jenkins && sudo systemctl enable jenkins. Access at http://your-server-ip:8080. Get the initial admin password: sudo cat /var/lib/jenkins/secrets/initialAdminPassword.

Complete setup wizard: Install suggested plugins, create your admin user, and configure the Jenkins URL. Install additional plugins: Docker Pipeline, GitHub Integration, Blue Ocean (modern UI).

Jenkins uses 'Jenkinsfile' — a text file defining your pipeline as code. This lives in your project's root directory alongside your source code, versioned with Git.

Create a Declarative Pipeline: pipeline { agent any; stages { stage('Build') { steps { sh 'echo Building...' } }; stage('Test') { steps { sh 'echo Testing...' } }; stage('Deploy') { steps { sh 'echo Deploying...' } } } }

In Jenkins UI: New Item → Pipeline → Name it → Under Pipeline section, choose 'Pipeline script from SCM' → Select Git → Enter your repository URL → Set branch to 'main'.

Trigger builds automatically: Configure webhooks in GitHub (Settings → Webhooks → Add → Payload URL: http://jenkins-url/github-webhook/). Now every push triggers a build.

Install Docker on your Jenkins server: sudo apt install docker.io -y && sudo usermod -aG docker jenkins && sudo systemctl restart jenkins. This lets Jenkins build Docker images.

Add a Dockerfile to your project: FROM node:18-alpine; WORKDIR /app; COPY package*.json ./; RUN npm install; COPY . .; EXPOSE 3000; CMD ['npm', 'start'].

Update Jenkinsfile to build Docker image: stage('Build Docker Image') { steps { sh 'docker build -t myapp:${BUILD_NUMBER} .' } }. The BUILD_NUMBER ensures unique image tags.

Add testing stage: stage('Test') { steps { sh 'npm test' } post { always { junit 'test-results/*.xml' } } }. Jenkins displays test results with pass/fail trends over time.

Add deployment stage: Deploy to a server via SSH, push Docker image to a registry (Docker Hub, AWS ECR), or deploy to Kubernetes. Start simple with: sh 'docker run -d -p 80:3000 myapp:${BUILD_NUMBER}'.

Add post-build actions: post { success { echo 'Build succeeded!' } failure { mail to: 'team@company.com', subject: 'Build Failed' } }. Integrate with Slack for instant notifications.

Set up Jenkins agents/nodes for parallel builds. Use Docker agents for clean, reproducible build environments: agent { docker { image 'node:18' } } — each build gets a fresh container.

Monitor your pipeline: Blue Ocean plugin provides beautiful visualization. Track build times, test coverage trends, and deployment frequency. Set up health checks for deployed applications.