Add self-hosted runner infrastructure with monitoring and security best practices

.github/IMPLEMENTATION_SUMMARY.md

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+# GitHub Actions & Self-Hosted Runners - Implementation Summary
+
+This document summarizes the comprehensive GitHub Actions workflows and self-hosted runner infrastructure implemented for this repository.
+
+## What Was Implemented
+
+### 1. Self-Hosted Runner Management Workflows
+
+#### `self-hosted-runner-setup.yml`
+- **Purpose:** Manual runner management and diagnostics
+- **Features:**
+  - Health checks on demand
+  - Runner information display
+  - System diagnostics (disk, memory, CPU)
+  - Instructions for runner configuration
+- **Trigger:** Manual (workflow_dispatch)
+
+#### `self-hosted-runner-health.yml`
+- **Purpose:** Automated runner health monitoring
+- **Features:**
+  - Scheduled weekly health checks (Mondays 9 AM UTC)
+  - Disk space monitoring with alerts
+  - Memory usage tracking
+  - Verification of required tools (Node.js, Yarn, Docker)
+  - Automatic cleanup of old artifacts
+- **Trigger:** Manual + Weekly schedule
+
+#### `self-hosted-example.yml`
+- **Purpose:** Reference implementation for self-hosted runner usage
+- **Features:**
+  - Dynamic runner selection (GitHub-hosted vs self-hosted)
+  - Mixed strategy (quick checks on GitHub-hosted, heavy builds on self-hosted)
+  - Examples for GPU workloads
+  - Integration test patterns
+  - Job dependency management
+- **Trigger:** Manual with configurable runner type
+
+### 2. Comprehensive Documentation
+
+#### `SELF_HOSTED_RUNNERS.md` (12.8 KB)
+Complete guide covering:
+- When to use self-hosted vs GitHub-hosted runners
+- Prerequisites and hardware requirements
+- Step-by-step setup instructions for Linux/macOS/Windows
+- Runner configuration (labels, groups, environment variables)
+- Security best practices (critical for production use)
+- Monitoring and maintenance procedures
+- Auto-scaling strategies (Kubernetes, cloud providers)
+- Troubleshooting common issues
+- Example workflow patterns
+
+#### `SELF_HOSTED_RUNNERS_QUICKSTART.md` (3.2 KB)
+Quick reference guide with:
+- Condensed setup steps
+- Essential commands
+- Security checklist
+- Common troubleshooting
+- Links to detailed documentation
+
+#### `workflows/README.md` (7.3 KB)
+Central documentation for all workflows:
+- Overview of all workflows in the repository
+- Trigger conditions and timeouts
+- Runner configurations
+- Best practices implementation
+- Usage instructions
+- Troubleshooting guide
+
+#### Updated `WORKFLOWS_BEST_PRACTICES.md`
+Added comprehensive section on:
+- When to use self-hosted runners
+- Self-hosted runner best practices
+- Security considerations
+- Monitoring strategies
+- Fallback patterns
+
+### 3. Enhanced .gitignore
+
+Added GitHub Actions runner-specific entries:
+```gitignore
+# GitHub Actions and Runners
+.github/actions-runner/
+actions-runner/
+_work/
+_diag/
+runner-config.local.yml
+.runner
+.credentials
+.credentials_rsaparams
+runner.env
+.env.runner
+```
+
+This prevents accidentally committing:
+- Runner binaries and configuration
+- Runner credentials
+- Work directories with sensitive data
+- Diagnostic files
+
+## Existing Workflows (Already Implemented)
+
+The repository already had excellent workflows following best practices:
+
+1. **node.js.yml** - Node.js CI (build & lint)
+2. **main.yml** - Unit tests
+3. **e2e-tests.yml** - End-to-end tests with Playwright
+4. **bearer.yml** - Security scanning
+5. **file-size-checker.yml** - Large file detection
+6. **update-algolia.yml** - Search index updates
+
+All existing workflows include:
+- ✅ Latest action versions (checkout@v4, setup-node@v4)
+- ✅ Explicit minimal permissions
+- ✅ Concurrency control
+- ✅ Appropriate timeouts
+- ✅ Efficient caching with Yarn
+
+## Security Highlights
+
+### Critical Security Practices Documented
+
+1. **Never use self-hosted runners for public repositories** ⚠️
+   - Malicious code in forks can compromise runners
+   - Clearly documented with warnings
+
+2. **Run runners as unprivileged users**
+   - Instructions for creating dedicated users
+   - Prevents privilege escalation
+
+3. **Network isolation**
+   - Firewall configuration guidance
+   - Proxy setup instructions
+
+4. **Ephemeral runners**
+   - Disposable runners for sensitive operations
+   - Configuration examples provided
+
+5. **Regular updates**
+   - Automated health monitoring
+   - Update procedures documented
+
+6. **Access control**
+   - Runner groups for organization-level access control
+   - Repository-specific runner configurations
+
+## Usage Patterns
+
+### For GitHub-Hosted Runners (Current Default)
+```yaml
+runs-on: ubuntu-latest
+```
+- All current workflows use this
+- Suitable for most standard operations
+- No additional setup required
+
+### For Self-Hosted Runners (When Configured)
+```yaml
+runs-on: [self-hosted, linux, x64]
+```
+- Opt-in per workflow/job
+- Requires runner setup (see docs)
+- Recommended for resource-intensive jobs
+
+### Mixed Strategy (Recommended)
+```yaml
+jobs:
+  quick-checks:
+    runs-on: ubuntu-latest  # Fast, minimal setup
+
+  heavy-build:
+    runs-on: [self-hosted, linux]  # Resource-intensive
+```
+
+## Getting Started with Self-Hosted Runners
+
+For users wanting to set up self-hosted runners:
+
+1. **Read the documentation**
+   - Start with `SELF_HOSTED_RUNNERS_QUICKSTART.md`
+   - Review security section in `SELF_HOSTED_RUNNERS.md`
+
+2. **Prepare infrastructure**
+   - Dedicated machine (VM or physical)
+   - Minimum 4 GB RAM, 20 GB disk
+   - Network access to GitHub
+
+3. **Follow setup guide**
+   - Repository Settings → Actions → Runners → New self-hosted runner
+   - Follow GitHub's provided commands
+   - Install required dependencies (Node.js, Yarn)
+
+4. **Test the setup**
+   - Run `self-hosted-runner-setup.yml` workflow
+   - Choose "health-check" action
+   - Verify all checks pass
+
+5. **Update workflows**
+   - Modify `runs-on` in workflows as needed
+   - Use `self-hosted-example.yml` as reference
+   - Test with small changes first
+
+## Monitoring and Maintenance
+
+### Automated Monitoring
+- Weekly health checks via `self-hosted-runner-health.yml`
+- Alerts for disk space, memory issues
+- Runner process verification
+
+### Manual Checks
+- On-demand via `self-hosted-runner-setup.yml`
+- Health check action
+- Runner information display
+
+### Maintenance Schedule
+- **Weekly:** Check runner status, review logs
+- **Monthly:** Update runner version, clean artifacts
+- **Quarterly:** Security audit, OS updates
+
+## Benefits
+
+### Current Setup (GitHub-Hosted)
+- ✅ Zero maintenance
+- ✅ Automatic updates
+- ✅ Isolated environments
+- ✅ Suitable for public repositories
+
+### With Self-Hosted Runners (When Configured)
+- ✅ Custom hardware/software
+- ✅ Network access to private resources
+- ✅ Cost optimization for high volumes
+- ✅ More resources (CPU, memory, disk)
+- ✅ Reduced queue times
+
+## File Structure
+
+```
+.github/
+├── workflows/
+│   ├── README.md                           # All workflows documentation
+│   ├── self-hosted-runner-setup.yml        # Manual runner management
+│   ├── self-hosted-runner-health.yml       # Automated health monitoring
+│   ├── self-hosted-example.yml             # Example implementation
+│   ├── node.js.yml                         # Existing: Build & lint
+│   ├── main.yml                            # Existing: Unit tests
+│   ├── e2e-tests.yml                       # Existing: E2E tests
+│   ├── bearer.yml                          # Existing: Security scan
+│   ├── file-size-checker.yml               # Existing: File size check
+│   └── update-algolia.yml                  # Existing: Search updates
+├── actions/
+│   └── setup-node-yarn/                    # Existing: Composite action
+├── WORKFLOWS_BEST_PRACTICES.md             # Enhanced: Added self-hosted section
+├── SELF_HOSTED_RUNNERS.md                  # New: Complete guide
+└── SELF_HOSTED_RUNNERS_QUICKSTART.md       # New: Quick reference
+```
+
+## Next Steps
+
+### Immediate (No Self-Hosted Runners Yet)
+- ✅ All workflows work with GitHub-hosted runners
+- ✅ Documentation is ready for future self-hosted setup
+- ✅ Example workflows demonstrate patterns
+- ✅ Monitoring infrastructure in place
+
+### When Ready to Add Self-Hosted Runners
+1. Review security requirements
+2. Provision hardware/VMs
+3. Follow setup guide
+4. Test with example workflow
+5. Uncomment self-hosted jobs in health monitoring
+6. Gradually migrate resource-intensive jobs
+
+## Conclusion
+
+This implementation provides:
+
+1. **Complete self-hosted runner infrastructure** ready to use when needed
+2. **Comprehensive documentation** covering all aspects of setup, security, and maintenance
+3. **Automated monitoring** to ensure runner health
+4. **Example workflows** demonstrating best practices
+5. **Enhanced security** through improved .gitignore
+6. **Flexibility** to use GitHub-hosted or self-hosted runners per workflow/job
+
+The repository now has enterprise-grade CI/CD infrastructure with clear paths for scaling as needs grow.