backend-observability

Observability for NestJS backends - structured pino logging with redaction and correlation ids via nestjs-cls, RED and USE metrics with low-cardinality Prometheus labels, OpenTelemetry tracing and context propagation across HTTP and queues, @nestjs/terminus liveness/readiness/startup health, SLIs/SLOs and symptom-based alerting, error tracking with PII scrubbing, audit versus application logs, dashboards and runbooks, tracing LLM and upstream calls, retention, testing, and performance triage. Load when adding logging, health endpoints, metrics, tracing, alerts, or debugging production behaviour.