What Is CI/CD? A Guide to Continuous Integration and Delivery

The era of "upload code to the server via FTP" is over. In modern software development, CI/CD ensures code reaches production safely and automatically.

Core Concepts

Continuous Integration (CI)

Developers frequently merge code into the main branch (multiple times daily), with automated tests running on every merge:

Developer Push → Build → Lint → Unit Test → Integration Test
                                              ↓
                                    ✅ Merge / ❌ Reject

Continuous Delivery (CD)

Code that passes CI is kept in a production-ready state at all times. Deploy to production with a single button click.

Continuous Deployment

Every change that passes tests is automatically deployed to production. No human intervention.

CI → CD (delivery) → Manual approval → Deploy
CI → CD (deployment) → Auto Deploy  ← This is the difference!

Why CI/CD?

| Metric | Before CI/CD | After CI/CD | |--------|-------------|-------------| | Deploy frequency | Monthly | Multiple per day | | Bug detection time | Days | Minutes | | Deploy success rate | 60-70% | 95%+ | | Rollback time | Hours | Seconds | | Manual testing effort | High | Minimal |

Pipeline Design

Stages of an ideal pipeline:

1. Source     → Detect code changes
2. Build      → Compile / create container image
3. Test       → Unit + Integration + E2E tests
4. Security   → SAST/DAST scanning
5. Staging    → Deploy to test environment
6. Approval   → Manual approval (optional)
7. Production → Deploy to production
8. Monitor    → Smoke test + monitoring

GitHub Actions Example

name: CI/CD Pipeline
on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
      - run: npm ci
      - run: npm run lint
      - run: npm test

  deploy:
    needs: test
    if: github.ref == 'refs/heads/main'
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: google-github-actions/deploy-cloudrun@v2
        with:
          service: myapp
          region: europe-west1

CI/CD Tools Compared

| Tool | Type | Advantage | Disadvantage | |------|------|-----------|-------------| | GitHub Actions | Cloud | GitHub integration, free tier | GitHub dependency | | GitLab CI | Cloud/Self-hosted | Built-in, comprehensive | Complex config | | Jenkins | Self-hosted | Flexible, plugin ecosystem | Maintenance overhead | | CircleCI | Cloud | Fast, simple | Cost | | Azure DevOps | Cloud | Enterprise, comprehensive | Microsoft ecosystem |

Best Practices

1. Automate Everything

Lint, test, build, deploy — no manual steps.

2. Fast Feedback

Pipeline should not exceed 10 minutes. Use parallel execution and caching.

3. Trunk-Based Development

Avoid long-lived branches. Make small, frequent merges.

4. Feature Flags

Put unfinished features behind flags. Deploy ≠ Release.

5. Rollback Strategy

Always have a mechanism to revert to the previous version.

Conclusion

CI/CD is non-negotiable in modern software development. It reduces risk, increases deployment speed, and multiplies team efficiency. It requires investment upfront but pays off from the first week.

Learn CI/CD pipeline design and DevOps practices with interactive missions on LabLudus.