# CI/CD Patterns

## Overview

Continuous Integration (CI) and Continuous Deployment (CD) automate the software delivery process, enabling frequent, reliable releases with minimal manual intervention.

## Core CI/CD Principles

### Continuous Integration
- **Merge Often**: Small, frequent commits
- **Automated Builds**: Build on every commit
- **Fast Feedback**: Quick test execution
- **Fail Fast**: Catch issues early

### Continuous Deployment
- **Automated Testing**: Comprehensive test suite
- **Automated Deployment**: Push to production automatically
- **Feature Flags**: Gradual feature rollouts
- **Monitoring**: Real-time production monitoring

## Common CI/CD Patterns

### Git Flow Integration

```yaml
# GitHub Actions example
name: CI
on:
  push:
    branches: [main, develop]
  pull_request:
    branches: [main, develop]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Setup Python
        uses: actions/setup-python@v4
        with:
          python-version: '3.10'
      - name: Install dependencies
        run: pip install -r requirements.txt
      - name: Ruff (lint)
        run: ruff check .
      - name: Ruff (format)
        run: ruff format --check .
      - name: Run tests
        run: pytest
```

### Branch-Based Workflows

**Main Branch:**
- Production-ready code
- Protected branch
- Requires review
- Full test suite

**Develop Branch:**
- Integration branch
- Automated tests
- Pre-production deployment

**Feature Branches:**
- Feature development
- Unit tests required
- Integration tests optional

### Build Strategies

**Multi-Stage Builds:**
```dockerfile
# Stage 1: Build
FROM python:3.10-slim as builder
WORKDIR /app
COPY requirements.txt .
RUN pip install --user -r requirements.txt

# Stage 2: Runtime
FROM python:3.10-slim
WORKDIR /app
COPY --from=builder /root/.local /root/.local
COPY . .
CMD ["python", "app.py"]
```

**Parallel Execution:**
- Run tests in parallel
- Build multiple artifacts simultaneously
- Reduce total build time

### Deployment Strategies

**Blue-Green Deployment:**
- Two identical production environments
- Switch traffic instantly
- Zero-downtime deployments
- Easy rollback

**Canary Releases:**
- Gradual rollout to subset of users
- Monitor metrics
- Expand if successful
- Rollback if issues

**Feature Flags:**
- Toggle features without deployment
- A/B testing capability
- Gradual feature rollout
- Instant rollback

## CI/CD Pipeline Stages

### 1. Source Control
- Version control (Git)
- Branch protection rules
- Commit message standards
- Code review requirements

### 2. Build Stage
- Dependency installation
- Compilation/transpilation
- Artifact creation
- Version tagging

### 3. Test Stage
- Unit tests
- Integration tests
- E2E tests
- Performance tests

### 4. Quality Checks
- Code linting
- Static analysis
- Security scanning
- Coverage reports

### 5. Build Artifacts
- Docker images
- Package archives
- Binary distributions
- Documentation

### 6. Deploy Stage
- Environment configuration
- Database migrations
- Service deployment
- Health checks

## Best Practices

### Fast Feedback
- Keep build times under 10 minutes
- Parallelize where possible
- Cache dependencies
- Optimize test execution

### Reliability
- Idempotent deployments
- Rollback procedures
- Health checks
- Monitoring and alerting

### Security
- Secrets management
- Dependency scanning
- Container scanning
- Access control

### Visibility
- Build status badges
- Deployment notifications
- Test results dashboard
- Performance metrics

## Common Tools

### CI/CD Platforms
- **GitHub Actions**: GitHub-integrated CI/CD
- **GitLab CI**: Built into GitLab
- **Jenkins**: Self-hosted automation
- **CircleCI**: Cloud-based CI/CD
- **Travis CI**: Continuous integration

### Build Tools
- **Docker**: Containerization
- **Buildpacks**: Automated container builds
- **Bazel**: Fast, scalable builds
- **Gradle**: Build automation

### Testing Tools
- **pytest**: Python testing
- **Jest**: JavaScript testing
- **Selenium**: Browser automation
- **Postman**: API testing

## Anti-Patterns to Avoid

1. **Manual Steps**: Automate everything
2. **Long Builds**: Optimize build times
3. **Flaky Tests**: Fix unstable tests
4. **No Rollback Plan**: Always have rollback
5. **Secret Hardcoding**: Use secrets management
6. **Skipping Tests**: Don't disable tests
7. **Monolithic Pipelines**: Break into stages
