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Add Application Performance Monitoring (APM) with Prometheus metrics

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- Backend: Implement Prometheus metrics collection
  - Add prometheus-client dependency
  - Create metrics utility module with HTTP request tracking counters, histograms, gauges
  - Implement MetricsMiddleware to track request latency, count, and active requests
  - Add /metrics endpoint to expose metrics in Prometheus text format
  - Normalize paths to prevent cardinality explosion (e.g., /api/{id} for UUIDs)
  - Exclude /metrics and /health from detailed tracking

- Frontend: Add web vitals and API metrics collection
  - Install web-vitals library (v4.0.0) for Core Web Vitals tracking
  - Create metrics utility module for FCP, LCP, CLS, INP, TTFB collection
  - Implement useTrackedFetch hook for automatic API call metrics (method, endpoint, status, duration)
  - Initialize web vitals tracking in App component on mount
  - Provide exportMetrics() for sending metrics to backend

- Testing:
  - Add comprehensive backend metrics tests (9 tests, 100% coverage)
  - Add comprehensive frontend metrics tests (10 tests)
  - All tests passing

- Documentation:
  - Expand Docs/Observability.md with complete APM section
  - Include metrics reference, integration examples (Prometheus, Datadog, NewRelic)
  - Add troubleshooting guide and best practices for cardinality management
  - Update Tasks.md to mark APM task as complete

Metrics exposed:
- bangui_http_requests_total: HTTP request count by method, endpoint, status
- bangui_http_request_duration_seconds: Request latency histogram
- bangui_http_active_requests: Active request gauge
- Web Vitals: CLS, FCP, INP, LCP, TTFB with ratings
- API metrics: endpoint, method, status, duration, timestamp

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
Lukas
2026-05-01 18:33:14 +02:00
parent 37078b742b
commit 1af67eb0ce
14 changed files with 969 additions and 74 deletions
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Docs/Tasks.md
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## [MEDIUM] No structured logging to external system
**Where found**
- Logs only go to stdout/file, no external aggregation
**Why this is needed**
Can't search across instances, historical logs lost on instance recycle.
**Goal**
Ship logs to centralized logging platform.
**What to do**
1. **Short-term:** Ensure `structlog` JSON output is valid (already done)
2. **Long-term:** Ship to logging platform (ELK, Datadog, Papertrail)
**Possible traps and issues**
- External logging adds latency
- Sensitive data must not be logged
- Log volume can be massive
**Docs changes needed**
- Add `Docs/Observability.md` section on logging
**Doc references**
- `Docs/Observability.md` (new)
---
## [MEDIUM] No Application Performance Monitoring (APM)
**Where found**
**Status: COMPLETED ✓**
- Backend: no metrics collection, latency tracking
- Frontend: no error tracking, performance metrics
- No observability into request performance
**What was done:**
- Backend Prometheus metrics: `/metrics` endpoint exposes request count, latency, active requests
- Frontend web-vitals tracking: FCP, LCP, CLS, INP, TTFB collection
- API call metrics: automatic tracking of latency and error rates
- Complete documentation with examples and integration guides
**Why this is needed**
**Implementation:**
- Backend: `app/utils/metrics.py`, `app/middleware/metrics.py`, `app/routers/metrics.py`
- Frontend: `src/utils/metrics.ts`, `src/hooks/useTrackedFetch.ts`
- Documentation: `Docs/Observability.md` (APM section)
Without metrics, blind in production: API slow? Unknown. Which endpoints fail most? Unknown.
**Goal**
Add comprehensive metrics collection and monitoring.
**What to do**
1. **Backend metrics:**
- Add Prometheus metrics: request count, latency, active requests
- Expose `/metrics` endpoint
2. **Frontend metrics:**
- Page load time, FCP, LCP using `web-vitals`
- API error rates and latencies
3. **Aggregation:**
- Prometheus + Grafana, or Datadog/NewRelic
**Possible traps and issues**
- Metrics collection has performance cost
- Cardinality explosion with tags
- PII in metrics
**Docs changes needed**
- Add `Docs/Observability.md`
**Doc references**
- `Docs/Observability.md` (new)
**Metrics exposed:**
- `bangui_http_requests_total` - HTTP request count by method, endpoint, status
- `bangui_http_request_duration_seconds` - Request latency histogram
- `bangui_http_active_requests` - Current active requests gauge
- Web Vitals: CLS, FCP, INP, LCP, TTFB
- API call metrics: method, endpoint, status, duration
---