🌍 Epic: Implement GitHub Actions support for platform portability

[kingdonb]

🎯 Epic: GitHub Actions Support for Platform Portability

Implement GitHub Actions workflow components equivalent to our GitLab CI pipeline, enabling hephy-builder to work seamlessly across both platforms.

📋 Current State

• ✅ GitLab CI: Full implementation in .gitlab-ci.yml (495 lines, production ready)
• ❌ GitHub Actions: Not yet implemented
• 📖 Design: PLATFORM_PORTABILITY.md contains initial architecture planning

🏗️ Architecture Vision

Component-Based Design

hephy-builder/
├── github/
│   ├── workflows/
│   │   ├── hephy-build.yml     # Reusable workflow
│   │   └── hephy-deploy.yml    # Optional deployment
│   └── actions/
│       ├── prepare/            # Change detection action
│       ├── build/              # Multi-arch build action
│       └── manifest/           # Manifest creation action
├── gitlab/
│   ├── hephy-build.yml         # Include template
│   └── components/             # Job templates
└── shared/
    ├── scripts/                # Platform-agnostic scripts
    └── configs/                # Default configurations

🔧 Implementation Phases

Phase 1: Core Workflow Translation

• Create GitHub Actions workflow equivalent to .gitlab-ci.yml
• Port prepare stage (change detection, architecture filtering)
• Implement multi-arch build jobs for GitHub-hosted runners
• Add manifest creation stage using existing manifest-tool

Phase 2: Reusable Actions

• Create kingdon-ci/hephy-builder-action repository
• Package prepare, build, and manifest stages as reusable actions
• Implement configuration abstraction layer
• Add comprehensive action documentation

Phase 3: Platform Abstraction

• Design .hephy/config.yaml format for platform-agnostic configuration
• Create conversion tools between GitLab CI and GitHub Actions
• Implement shared script library for platform independence
• Add platform detection and adaptation logic

Phase 4: Enterprise Features

• Self-hosted runner support (GitHub Enterprise)
• Custom registry configuration
• Advanced security and compliance features
• Integration with enterprise CI/CD systems

📊 Technical Requirements

GitHub Actions Workflow Features

• Multi-arch support: Leverage GitHub's runs-on matrix for amd64/arm64
• ECR authentication: AWS configure-credentials action integration
• Change detection: Port hack/prepare_diff.sh to GitHub context
• Artifact management: Use GitHub Actions artifacts for build coordination
• Conditional execution: Smart job skipping based on architecture needs

Backward Compatibility

• ✅ Zero breaking changes: Existing GitLab CI continues unchanged
• ✅ Configuration compatibility: Same build-config.yaml format
• ✅ Registry support: All existing destinations (ECR, Docker Hub, etc.)

🎯 Success Criteria

Functional Parity

• GitHub Actions workflow builds identical images to GitLab CI
• Multi-arch manifest creation works correctly
• Change detection and architecture filtering functional
• Performance comparable to GitLab CI pipeline

Developer Experience

• Drop-in GitHub Actions component for any repository
• Clear migration guide from GitLab CI to GitHub Actions
• Comprehensive documentation and examples
• One-command setup for new repositories

Testing Validation

• Successful builds on GitHub-hosted runners
• Multi-arch image validation
• Registry push/pull verification
• End-to-end workflow testing

🔗 Related Issues

This epic supports:

• Issue Epic: Transform to hephy-builder with multi-platform CI support #10: Transform to hephy-builder with multi-platform CI support
• Issue Add Spin (WebAssembly) build backend support #11: Spin backend support (needs GitHub Actions)
• Issue Add Ko build backend for optimized Go application builds #12: Ko backend support (benefits from GitHub Actions)
• PR 🚀 Transform kaniko-builder to hephy-builder: Resurrect "git push deis main" with Modern Tooling #13: hephy-builder transformation

💡 Implementation Strategy

Incremental Development

1. Start with simple workflow: Single-arch builds first
2. Add multi-arch support: Leverage GitHub's runner matrix
3. Extract reusable actions: Package for community use
4. Add platform abstraction: Support both GitLab and GitHub

Community Impact

• Lower barrier to entry: GitHub Actions more accessible than GitLab CI
• Broader adoption: Tap into GitHub's massive developer base
• Enterprise appeal: Support both major Git platforms
• Open source growth: Easier for contributors to test and contribute

📚 Resources

GitHub Actions Documentation

• Workflow syntax
• Multi-architecture builds
• Custom actions

Reference Implementations

• Existing GitLab CI pipeline (.gitlab-ci.yml)
• hack/prepare_diff.sh change detection logic
• Multi-arch manifest creation patterns

Testing Infrastructure

• GitHub-hosted runners (amd64/arm64)
• ECR registry access
• Test repositories for validation

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This is a high-impact issue that transforms hephy-builder from "GitLab-only" to "platform-portable" - a key differentiator in the modern CI/CD landscape.