CI/CD Pipelines

CI/CD Pipelines

Why Engineers Care About This

CI/CD pipelines automate testing and deployment, enabling fast, reliable releases. Continuous Integration (CI) runs tests on every commit, catching bugs early. Continuous Deployment (CD) automates deployment to production, enabling frequent releases. But pipelines require careful design—testing strategies, deployment automation, and safety gates. Understanding CI/CD helps you build reliable deployment processes.

When deployments are manual and error-prone, or bugs reach production, or releases take days instead of hours, you're hitting CI/CD problems. These problems compound. Without CI/CD, deployments require manual steps (error-prone, slow). Without proper testing, bugs reach production. Good CI/CD solves these problems by automating testing and deployment.

In interviews, when someone asks "How would you set up deployment for this system?", they're really asking: "Do you understand CI/CD? Do you know how to design pipelines? Do you understand testing strategies and deployment automation?" Most engineers don't. They set up basic pipelines without understanding stages, or avoid CI/CD because it's "too complex."

Core Intuitions You Must Build

• CI runs tests on every commit, CD automates deployment. Continuous Integration (CI) runs automated tests on every commit, catching bugs early. Continuous Deployment (CD) automates deployment to production after tests pass. CI is about catching bugs early, CD is about deploying frequently. Don't confuse them—CI is testing, CD is deployment. Also, you can have CI without CD (manual deployment), but CD requires CI (must test before deploying).

• Pipeline stages should run in order with proper gates. Pipelines have stages: build, test, deploy. Stages run in order, and gates (test results, approvals) control progression. If a stage fails, pipeline stops (don't deploy broken code). Design pipelines with proper gates—test failures should block deployment, manual approvals for production. Don't skip stages or gates—they prevent bad deployments.

• Parallel execution speeds up pipelines. Pipelines often have independent stages (unit tests, integration tests, linting) that can run in parallel. Running stages in parallel speeds up pipelines (minutes instead of hours). But parallel execution requires careful design—stages must be independent, and resource usage must be managed. Don't run everything sequentially—parallelize independent stages.

• Testing strategies should match deployment frequency. If you deploy frequently (multiple times per day), you need fast tests (unit tests, integration tests) that run quickly. If you deploy less frequently (weekly), you can run slower tests (end-to-end tests, performance tests). Design testing strategies based on deployment frequency—fast tests for frequent deployments, comprehensive tests for less frequent deployments.

• Secrets and environment configuration must be handled securely. Pipelines need secrets (API keys, database passwords) and environment configuration. Don't hardcode secrets in pipeline code—use secret management (secrets managers, environment variables). Also, don't log secrets—they appear in pipeline logs. Handle secrets securely—inject at runtime, not in code.

• Deployment strategies enable safe production releases. Different deployment strategies (blue-green, canary, rolling) enable safe releases. Blue-green: deploy new version alongside old, switch traffic. Canary: deploy to small percentage, gradually increase. Rolling: update gradually, one instance at a time. Choose based on your needs—blue-green for zero downtime, canary for risk reduction, rolling for simplicity.

Subtopics (Taught Through Real Scenarios)

CI vs CD

What people usually get wrong:

Engineers often confuse CI and CD. But they're different: CI is about testing (run tests on every commit), CD is about deployment (automate deployment after tests pass). You can have CI without CD (manual deployment), but CD requires CI (must test before deploying). Don't confuse them—CI catches bugs, CD deploys code.

How this breaks systems in the real world:

A team set up CI (automated testing) but deployed manually. Tests caught bugs, but deployments were still manual and error-prone. The team wanted faster deployments but didn't automate them. The fix? Add CD—automate deployment after tests pass. Now deployments are fast and reliable. But the real lesson is: CI and CD are different. CI catches bugs, CD automates deployment.

What interviewers are really listening for:

They want to hear you talk about CI vs CD, their purposes, and their relationship. Junior engineers say "CI/CD is just automation." Senior engineers say "CI runs tests on every commit to catch bugs early, CD automates deployment after tests pass—CI is about testing, CD is about deployment, and CD requires CI." They're testing whether you understand that CI and CD are separate but related concepts.

Pipeline Design and Stages

What people usually get wrong:

Engineers often design pipelines without proper stages or gates. But pipelines should have clear stages (build, test, deploy) with gates (test results, approvals) controlling progression. If a stage fails, pipeline should stop (don't deploy broken code). Design pipelines with proper gates—test failures should block deployment, manual approvals for production.

How this breaks systems in the real world:

A pipeline had stages but no gates. When tests failed, pipeline continued and deployed broken code to production. Bugs reached production, causing outages. The fix? Add gates—if tests fail, stop pipeline and don't deploy. Also, add manual approval gate for production deployments. Now broken code doesn't reach production. But the real lesson is: pipeline gates prevent bad deployments. Don't skip gates.

What interviewers are really listening for:

They want to hear you talk about pipeline stages, gates, and failure handling. Junior engineers say "just run build, test, deploy." Senior engineers say "design pipelines with clear stages (build, test, deploy) and gates (test results, approvals)—if a stage fails, stop pipeline to prevent bad deployments." They're testing whether you understand that pipelines are about safety, not just automation.

Testing Strategies in Pipelines

What people usually get wrong:

Engineers often run all tests in pipelines, regardless of deployment frequency. But testing strategies should match deployment frequency. If you deploy frequently (multiple times per day), you need fast tests (unit tests, integration tests) that run quickly. If you deploy less frequently (weekly), you can run slower tests (end-to-end tests, performance tests). Design testing strategies based on deployment frequency.

How this breaks systems in the real world:

A pipeline ran all tests (unit, integration, end-to-end, performance) on every commit. Tests took 2 hours to complete, blocking deployments. The team wanted to deploy multiple times per day but couldn't (pipeline too slow). The fix? Run fast tests (unit, integration) on every commit, run slow tests (end-to-end, performance) on schedule or before production deployment. Now deployments are fast. But the real lesson is: testing strategies should match deployment frequency. Fast tests for frequent deployments.

What interviewers are really listening for:

They want to hear you talk about testing strategies, test speed, and deployment frequency. Junior engineers say "just run all tests." Senior engineers say "design testing strategies based on deployment frequency—fast tests (unit, integration) for frequent deployments, comprehensive tests (end-to-end, performance) for less frequent deployments." They're testing whether you understand that testing is about balance, not just "running all tests."

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• CI runs tests on every commit, CD automates deployment—CI catches bugs, CD deploys code
• Pipeline stages should run in order with proper gates—test failures should block deployment
• Parallel execution speeds up pipelines—run independent stages in parallel
• Testing strategies should match deployment frequency—fast tests for frequent deployments
• Secrets and environment configuration must be handled securely—use secret management, don't hardcode
• Deployment strategies enable safe production releases—blue-green, canary, rolling
• Good CI/CD enables fast, reliable, automated releases

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• Docker & Containerization - Building container images in CI/CD
• Kubernetes - Deploying to Kubernetes with CD
• Infrastructure as Code - Managing infrastructure in pipelines