CI/CD: Automating Testing and Deployment

The goal of a modern developer is to automate everything. You should never manually upload code to a server. Instead, you use a CI/CD Pipeline.

• CI (Continuous Integration): Every time you push code, a server automatically runs your tests (Module 14).
• CD (Continuous Deployment): If the tests pass, the server automatically deploys the new version to the cloud.

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1. The GitHub Actions Workflow

GitHub Actions is the standard for CI/CD in the Python world. You define your pipeline in a YAML file in .github/workflows/.

name: Python CI

on: [push]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Set up Python
        uses: actions/setup-python@v4
        with:
          python-version: '3.11'
      - name: Install dependencies
        run: pip install -r requirements.txt
      - name: Run tests
        run: pytest

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2. Secrets in CI/CD

Just like in your app, your CI/CD pipeline needs secrets (like your AWS keys or Docker Hub password). You store these in the GitHub Settings > Secrets page, and they are injected into the workflow at runtime.

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3. The "Stage before Production" Pattern

Never deploy directly to your main website.

1. Stage 1: Run Tests.
2. Stage 2: Deploy to a Staging Environment (a hidden version of your site for testing).
3. Stage 3: If Staging looks good, "Promote" it to Production.

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4. Zero-Downtime Deployment

Using tools like Blue-Green Deployment or Rolling Updates (standard in Kubernetes), you can update your API without a single second of downtime for your users. The old version stays running until the new version is confirmed healthy.

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Visualizing the Pipeline

graph LR
    A["Push to Main"] --> B["GitHub Action Starts"]
    B --> C["Install Deps"]
    C --> D["Run Pytest"]
    D -- "Fail" --> E["Email Developer (Fix manual)"]
    D -- "Pass" --> F["Build Docker Image"]
    F --> G["Deploy to AWS/GCP"]

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Summary

• Automation: Removes human error from the deployment process.
• CI: Keeps your main branch always "Healthy."
• Secrets Manager: Securely handles cloud credentials.
• Zero-Downtime: The hallmark of a professional infrastructure.

In the next lesson, we wrap up Module 17 with Exercises on deployment architecture.

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Exercise: The Pipeline Guard

You just pushed a piece of code with a major bug.

1. If your CI/CD pipeline is set up correctly, will the bug make it to your live website?
2. Which part of the pipeline (Install, Test, Build, or Deploy) will catch the error?