The logging and monitoring service has been created

docs/logging-monitoring.md

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+# Logging & Monitoring in MyFanss Backend
+
+## Logging
+
+- Uses Winston via `AppLogger` service (see `src/logger/app-logger.service.ts`).
+- Log levels: info, warn, error, debug.
+- Context: timestamps, class/method, request info (where available).
+- Format: JSON in production, human-readable in development.
+- Usage:
+  ```typescript
+  import { AppLogger } from '../logger/app-logger.service';
+  // ...
+  constructor(private readonly logger: AppLogger) {}
+  this.logger.log('message', 'Context');
+  this.logger.error('error', 'stack', 'Context');
+  ```
+- GlobalExceptionFilter logs all errors.
+- No sensitive data should be logged.
+
+## Monitoring
+
+- Prometheus metrics exposed at `/metrics` (see `src/monitoring/monitoring.module.ts`).
+- Health checks (optional) at `/health` (see `src/monitoring/health.module.ts`).
+- Metrics include request count, duration, error rates, uptime, memory usage.
+
+## Configuration
+
+- Log level and format are environment-based (`NODE_ENV`).
+- Logging can be filtered by changing Winston config in `app-logger.service.ts`.
+
+## Example
+
+See `AppController` for logger usage example.
+
+## Extending
+
+- Use `AppLogger` in any service/controller for consistent logging.
+- Add custom metrics using Prometheus decorators if needed.
+
+---
+For questions, contact the backend team.