CI/CD (Continuous Integration / Continuous Deployment)

CI/CD explained: Without CI/CD, developers merge code manually, test locally, and deploy by hand (slow, error-prone). With CI/CD, every code push triggers automated tests, and passing builds deploy automatically (fast, reliable). Continuous Integration (CI): Developers push code to a shared repository (GitHub, GitLab). CI server (GitHub Actions, CircleCI, Jenkins) runs automated tests on every push. If tests pass, code merges. If tests fail, developer fixes it. Catch bugs early before they reach production. Continuous Deployment (CD): After code passes CI tests, it auto-deploys to staging or production. No manual deployment steps. Deploy 10 times a day instead of once a week. Faster iteration, faster feedback, less deployment risk (small changes are safer than big releases). CI vs. CD vs. Continuous Delivery: CI = automated testing. Continuous Delivery = code is always ready to deploy but requires manual approval. Continuous Deployment = code auto-deploys to production with zero human intervention. CD is the most aggressive—high trust in automation required. Why CI/CD matters for startups: (1) Ship faster—deploy in minutes, not days, (2) Reduce bugs—automated tests catch regressions, (3) Improve developer experience—no manual deployment stress, (4) Enable experimentation—deploy, measure, iterate quickly. CI/CD tools: GitHub Actions (integrated with GitHub), CircleCI (popular for complex pipelines), Jenkins (open-source, self-hosted), GitLab CI (integrated with GitLab), Vercel/Netlify (frontend-focused, instant deploys). Most modern tools are free for small teams. CI/CD pipeline stages: (1) Code commit → (2) Run tests (unit, integration, e2e) → (3) Build artifacts (Docker image, compiled assets) → (4) Deploy to staging → (5) Run smoke tests → (6) Deploy to production → (7) Monitor errors. Each stage is automated. Common mistakes: (1) No tests—CI/CD without tests is just automation, not quality assurance, (2) Flaky tests—unreliable tests slow down pipelines and erode trust, (3) Long pipelines—if tests take 30 minutes, CI/CD feels slow, (4) No rollback plan—auto-deploy is risky without easy rollback.

Stripe deploys to production multiple times per day using CI/CD. Every commit runs automated tests; passing commits auto-deploy. Netflix uses CI/CD to deploy thousands of times per day across microservices.