Frontend Gateway Module - Wiz-DevTech/prettygirllz GitHub Wiki

Here’s a comprehensive README.md for your Frontend Gateway Module, including setup instructions, testing scenarios, and error handling workflows:

# Frontend Gateway Module

A modular gateway handling SSR, API composition, client adaptors, and error recovery for web/mobile clients.

## Features
- **SSR Templates**: JSP-based server-side rendering with fallback cache.
- **API Composition Layer**: Aggregation, transformation, retries, and circuit breaking.
- **Client-Side Adaptors**: Device-specific (web/mobile) response tailoring.
- **Error Handling**: Monitoring, fallbacks, and recovery workflows.
- **Monitoring**: Real-time dashboard with SLO tracking.

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## Prerequisites
- Java 11+ (for SSR/JSP)
- Node.js 16+ (for client adaptors)
- Docker (for monitoring stack)
- Redis (for fallback cache)

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## Installation
```bash
# Clone the repo
git clone https://github.com/your-repo/frontend-gateway.git
cd frontend-gateway

# Install dependencies
./gradlew build  # For SSR/ACL
npm install      # For client adaptors

# Start services
docker-compose up -d  # Monitoring stack (Prometheus/Grafana/ELK)

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Configuration

1. API Composition Layer

Edit config/acl.yml:

circuit_breaker:
  failure_threshold: 50%  # Trip after 50% errors
  retry:
    max_attempts: 3
    backoff: 1000ms

2. Error Handling

Set fallbacks in config/error-handling.yml:

fallbacks:
  ssr:
    enabled: true
    ttl: 300s  # 5-minute cache
  client:
    mobile: "offline.html"
    web: "error-500.html"

3. Monitoring

Configure dashboards in monitoring/grafana/provisioning/dashboards/frontend.json.

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Testing

Unit Tests

./gradlew test  # SSR/ACL tests
npm test        # Client adaptors

Integration Tests

Simulate errors using MockServer:

# Start mock API with failure modes
docker run -d --name mock-api -p 1080:1080 mockserver/mockserver

Test Scenarios

Test Case	Command	Expected Result
SSR Fallback	curl -H "Accept: text/html" http://localhost:8080?trigger_error=500	Serves cached content
API Retry	curl -H "Accept: application/json" http://localhost:8080/api?retry=true	Retries 3x before failing
Mobile Offline	curl -H "User-Agent: iPhone" http://localhost:8080?network=offline	Shows offline UI

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Error Recovery Workflows

Manual Recovery

1. Retry API Call:

   // Client-side adaptor example
   async function fetchWithRetry(url, retries = 3) {
     try {
       return await fetch(url);
     } catch (err) {
       if (retries > 0) await fetchWithRetry(url, retries - 1);
       else showFallbackUI();
     }
   }
   

2. SSR Rehydration:

   # Force cache refresh
   POST /ssr-cache/refresh
   

Automated Recovery

• Circuit Breaker: Automatically restores after 30s.
• Monitoring Alerts: Triggers Slack/PagerDuty on SLO violation.

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Monitoring Dashboard

Access at http://localhost:3000/d/frontend (Grafana):

• Key Metrics:
  • http_errors{status=~"5.."}: Server error rate
  • ssr_fallback_requests_total: Fallback activations
  • client_adaptor_errors{device="mobile"}: Mobile failures

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Troubleshooting

Symptom	Debug Command	Solution
SSR cache not updating	curl -v http://localhost:8080/cache/status	Check Redis connection
API aggregation slow	docker logs acl-service	Optimize ACL query parallelism
Missing mobile errors	kubectl logs -l app=client-adaptor	Verify User-Agent parsing

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License

Apache 2.0

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### Key Sections Explained:
1. **Testing**: Ready-to-run commands for simulating errors (5xx, offline mode).
2. **Recovery Workflows**: Code snippets for client-side retries and SSR cache management.
3. **Monitoring**: Preconfigured Grafana dashboard with SLO tracking.
4. **Troubleshooting**: Quick-reference table for common issues.

To use this:
1. Save as `README.md` in your project root.
2. Update links/ports as needed.
3. Add real screenshots for the dashboard preview. 

Would you like me to add:
1. **Load testing** instructions (e.g., Locust/K6)?
2. **Security** considerations (rate limiting, auth)?
3. **Deployment** guides (Kubernetes, AWS)?