🔗CI/CD Demystified

🔁 Continuous Integration (CI)

Goal: Catch bugs early during development.

📌 What it means:
Every time you or your team writes code and pushes to Git, automated tests, linters, and build scripts run automatically.

🧪 Includes:

• Unit tests

• Lint checks

• Build checks

🛠️ Tools:

• GitHub Actions, Jenkins, CircleCI, GitLab CI

📦 Example:
You push a login feature to GitHub → GitHub Actions runs tests → If everything passes, the code is ready for staging.

🚚 Continuous Delivery (CD)

Goal: Always have a production-ready codebase.

📌 What it means:
After CI, your code can be manually deployed anytime — it’s always ready to ship.

✅ Run tests not just on main, but on every commit (feature branches too).

🛠️ Tools:

• Spinnaker, GitLab, ArgoCD, Flux

📦 Example:
You fix a bug → GitHub Actions runs tests → code is merged to main → a button in the dashboard lets the team deploy it to prod when ready.

🚀 Continuous Deployment (CD)

Goal: Automatically deploy every successful commit to production — no human click needed.

📌 What it means:
Once code passes all tests + security checks → it's pushed live for users.

🧪 Still, there’s risk of bugs (even with 99% test coverage), so smart deployment strategies are used:

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Deployment Strategies

1. Canary Deployment

Rollout to a small subset of users (e.g., 5% → 10% → 50% → 100%)
🟢 Safer → Easy to rollback if bugs detected

📦 Example:
Your new UI is first shown to only 10% of users. You monitor errors & feedback. If it’s smooth, rollout increases.

🛠️ Tools:

• LaunchDarkly, Argo Rollouts, Istio, Flagger

2. Blue-Green Deployment

Two environments:

• Blue = current version

• Green = new version

📌 Users are gradually shifted from Blue → Green.

🧪 You test Green → Switch DNS/load balancer → Done!

📦 Example:
New checkout flow is deployed to Green. You test it live while users are still on Blue. Once verified, you flip the switch.

🛠️ Tools:

• Kubernetes, NGINX, AWS CodeDeploy, Spinnaker

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🎯 Final Real-World Flow

1. Developer pushes code → CI (GitHub Actions runs tests)

2. CD kicks in → Auto deploys to staging → Manual/Auto deploy to prod

3. Canary rollout begins → Monitored via dashboards

4. If smooth → 100% rollout

5. Issues? → Rollback or redirect traffic to older version (Blue)

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Using Jenkins for CI/CD & Deployment

Jenkins is one of the most widely-used automation servers for CI/CD. It’s open-source, highly customizable, and integrates with almost everything.

🛠️ Jenkins Pipeline Flow:

Let’s say you're deploying a new login feature:

🧱 Step-by-step Jenkins Setup:

1. 🧑‍💻 Developer pushes code to GitHub.

2. 🧪 Jenkins Job (CI) triggers automatically:

   • Pulls code

   • Runs unit tests

   • Linting

   • Builds the app (maybe Docker image)

3. ✅ If CI passes, Jenkins moves to CD pipeline:

   • Deploys to Staging server

   • Runs integration tests

   • Sends approval request (for Continuous Delivery) OR

   • Auto deploys to Production (for Continuous Deployment)

Tools Jenkins Works With:

• GitHub/GitLab/Bitbucket – Code repo

• Docker – Build & push images

• Kubernetes – Container orchestration

• ArgoCD/Spinnaker – Rollouts

• Slack/Email – Notifications

• SonarQube – Code quality check

Final Summary (CI/CD with Jenkins):

Thanks for reading!