CI/CD Fundamentals: Jenkins, GitLab CI, GitHub Actions, and ArgoCD

Modern software development thrives on speed, automation, and reliability—and that's where CI/CD comes in. If you're looking to ship features faster without breaking your app, you need a solid grasp of Continuous Integration and Continuous Deployment/Delivery.

In this article, we’ll explore what CI/CD is, why it matters, and how popular tools like Jenkins, GitLab CI, GitHub Actions, and ArgoCD help bring automation to life.

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🚀 What Is CI/CD?

CI/CD stands for:

• Continuous Integration (CI): Automatically building and testing code every time a developer pushes changes.

• Continuous Deployment/Delivery (CD): Automatically releasing code to production (or staging) after it passes all tests.

Together, CI/CD helps teams release faster, reduce bugs, and increase confidence in production deployments.

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🔁 The CI/CD Pipeline at a Glance

A typical pipeline includes:

1. Code push → triggers CI

2. Build → compile, bundle, containerize

3. Test → unit, integration, linting

4. Package → artifact creation (e.g., Docker image)

5. Deploy → staging/production

6. Monitor → observe performance, roll back if needed

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🧰 Popular CI/CD Tools Overview

1. Jenkins

• Type: Open-source automation server

• Strengths:

  • Highly customizable with plugins

  • Large community support

  • Good for self-hosted, complex workflows

• Use Case:

  • Enterprises with legacy or hybrid infrastructure

• Example:

groovy
pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        sh 'make build'
      }
    }
    stage('Test') {
      steps {
        sh 'make test'
      }
    }
  }
}

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2. GitLab CI/CD

• Type: Built-in to GitLab

• Strengths:

  • Tight integration with Git repositories

  • Easy to configure via .gitlab-ci.yml

  • Built-in Docker, Kubernetes support

• Use Case:

  • Teams already using GitLab for version control

• Example:

yaml
stages:
  - build
  - test

build:
  script: make build

test:
  script: make test

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3. GitHub Actions

• Type: Native CI/CD for GitHub repositories

• Strengths:

  • Easy setup, reusable workflows

  • GitHub-native integration

  • Great community-maintained actions

• Use Case:

  • Open-source and small-to-medium teams on GitHub

• Example:

yaml
name: CI

on: [push]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - run: npm install
      - run: npm test

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4. ArgoCD (for CD only)

• Type: Kubernetes-native continuous delivery tool

• Strengths:

  • GitOps approach (Git is the source of truth)

  • Real-time sync with Kubernetes

  • Declarative configuration

• Use Case:

  • Teams deploying microservices to Kubernetes

• How It Works:

  • ArgoCD monitors a Git repository

  • When changes are detected, it applies them to the cluster

• Helm/Kustomize support out of the box

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🧪 CI/CD Use Cases

Scenario	Best Tool
Monorepo on GitHub	GitHub Actions
Microservices on Kubernetes	GitHub Actions + ArgoCD
Full DevOps with GitLab	GitLab CI/CD
Complex pipelines with legacy	Jenkins
Kubernetes GitOps	ArgoCD

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🔒 CI/CD Best Practices

• ✅ Run tests in parallel to speed up feedback

• ✅ Use separate environments: dev → staging → prod

• ✅ Automate rollbacks and alerting

• ✅ Scan for security and vulnerabilities

• ✅ Use secrets managers (not hardcoded keys!)

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📌 Conclusion

CI/CD is a cornerstone of modern DevOps, enabling fast, reliable, and automated software delivery. Whether you're building simple apps or orchestrating Kubernetes clusters, there’s a CI/CD tool that fits your workflow.

Key takeaway: Start simple, iterate often, and let automation do the heavy lifting.