Day 12 - Introduction to CI/CD

🎯 What is CI/CD?

CI/CD stands for Continuous Integration and Continuous Delivery/Deployment.

It is a set of practices and automated processes that help teams build, test, and deliver software efficiently and reliably.

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🧩 Why CI/CD is Needed

Before CI/CD, teams deployed applications manually — testing, scanning, and deploying took weeks or months.

With modern applications, users expect updates every few days or even hours, so companies must:

• Deliver software quickly and safely

• Ensure code quality and security

• Reduce human effort and error

👉 CI/CD automates these steps.

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⚙️ CI (Continuous Integration)

Continuous Integration is the process of automatically building and testing code whenever developers make changes.

Steps involved:

1. Code Commit: Developers push code to a Version Control System (VCS) such as GitHub, GitLab, or Bitbucket.

2. Build Process: The code is automatically compiled or built (e.g., using Maven for Java).

3. Unit Tests: Automated unit tests verify small pieces of functionality.

4. Static Code Analysis: Tools check for syntax errors, unused variables, and poor code practices (e.g., using SonarQube).

5. Code Quality & Security Scan: Tools detect vulnerabilities and ensure secure code.

✅ CI ensures that new code integrates smoothly with the existing codebase and remains stable.

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🚀 CD (Continuous Delivery / Deployment)

After successful integration, the Continuous Delivery phase automates:

1. Functional / Integration Testing: Ensures new code doesn’t break other features.

2. Report Generation: Summarizes test results, code quality, and coverage.

3. Deployment: Pushes code to environments like Dev, Staging, or Production.

Continuous Deployment goes one step further — automatically deploying to production without manual approval.

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🧠 How CI/CD Works (Step-by-Step Example)

1. A developer writes code locally (e.g., an addition feature in a calculator app).

2. After testing locally, they push the code to a Git repository.

3. A CI/CD tool (e.g., Jenkins, GitHub Actions, GitLab CI) detects the change.

4. The tool triggers a pipeline — a series of automated steps:

   • Build the code

   • Run tests (unit, functional)

   • Perform code analysis

   • Generate reports

   • Deploy to servers (Dev → Staging → Production)

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🧰 Common CI/CD Tools

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🏗️ Example: Jenkins (Legacy CI/CD Tool)

Jenkins Workflow:

1. Developer commits code → GitHub repository.

2. Jenkins detects the change (via webhook).

3. Jenkins runs a Pipeline consisting of:

   • Build (Maven)

   • Unit Tests (JUnit)

   • Code Quality (SonarQube)

   • Reporting (Allure)

   • Deployment (to Kubernetes, EC2, etc.)

Jenkins as an Orchestrator

• Jenkins integrates all tools together.

• Pipelines can be written in Groovy (Declarative or Scripted Pipeline syntax).

• Used widely for years, but has scaling limitations.

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🧭 Environments in CI/CD

Pipelines promote code automatically:

Dev → Staging → Production

Using manual approvals or automated policies.

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⚠️ Limitations of Jenkins (Legacy Approach)

• Requires manual setup of master and multiple worker nodes.

• Scaling to handle hundreds of microservices becomes complex and expensive.

• Continuous usage of compute resources (RAM/CPU), even when idle.

• Difficult to achieve zero-resource usage when pipelines are inactive.

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🌐 Modern CI/CD Solutions

Modern applications (like Kubernetes, Amazon, Flipkart) handle hundreds or thousands of microservices — they need scalable, on-demand CI/CD systems.

Example: Kubernetes Project on GitHub

• Uses GitHub Actions for automation.

• When a developer makes a pull request, a workflow runs automatically.

• Containers (pods) are created temporarily to execute build/test steps.

• After completion, the containers auto-delete → no wasted resources.

✅ Benefits:

• Zero compute waste when idle

• Shared runners for multiple projects

• Fast scaling (pods start instantly)

• Event-driven automation (no manual trigger)

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⚡ Modern CI/CD Tools

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🔁 Jenkins vs GitHub Actions — Quick Comparison

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🧩 Summary

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✅ In short:

CI/CD automates how your code goes from a developer’s laptop → through build, test, and security checks → to production servers — ensuring every release is fast, reliable, and safe.