Common Observability

---
name: common-observability
description: "Standards for structured logging, distributed tracing, and metrics. (triggers: **/*.service.ts, **/*.handler.ts, **/*.middleware.ts, **/*.interceptor.ts, **/*.go, **/*.java, **/*.kt, **/*.py, logging, tracing, metrics, opentelemetry, observability, slo)"
---

# Common Observability Standards

## **Priority: P1 (OPERATIONAL)**

## 📋 Logging & Tracing

- **JSON Logs**: Always emit JSON structured logs. Never plain-text in prod.
- **Correlation**: Extract `X-Request-Id` or `traceparent`. Attach to async context.
- **Tracing**: Use OpenTelemetry. Propagate W3C `traceparent`. 
- **Spans**: Name spans like `<HTTP_METHOD> <route>` (`GET /users/:id`).

## 📊 Metrics

- **Required**: Request rate, Error rate, Latency histogram (p50/p95/p99), Saturation.
- **SLOs**: Alert on SLO burn rates, not raw threshold spikes.

## 🚫 Anti-Patterns

- **Console.log**: Do not use in prod; use a structured logger (`pino`, `zap`).
- **PII in Logs**: Never log tokens, passwords, or full request bodies.
- **Dynamic Span Names**: `GET /users/123` causes cardinality explosion. Use `GET /users/:id`.
- **Missing Cleanup**: Always end tracing spans.

## References
- [Observability Data Formats](references/observability-formats.md)