Logging & Observability

Structured logging, distributed tracing, and metrics for production systems. Covers the full observability stack from log formatting to alert routing.

When to Use

Activate on: "structured logging", "distributed tracing", "OpenTelemetry", "OTel", "correlation ID", "log levels", "Grafana dashboard", "alerting thresholds", "SLI SLO", "Prometheus metrics", "PagerDuty integration", "observability stack", "Winston setup", "Pino logger", "log aggregation", "Datadog", "Honeycomb"

NOT for: Performance profiling (CPU/memory flamegraphs) | Load testing | Database query optimization | Security auditing

Decision Tree: What to Log at Each Level

flowchart TD
    E[Event Occurs] --> Q1{Does it represent\na system failure?}
    Q1 -->|Yes| Q2{Is it recoverable\nwithout human?}
    Q2 -->|No| FATAL[FATAL: Service cannot\ncontinue — trigger pager]
    Q2 -->|Yes| ERROR[ERROR: Operation failed,\nwill retry or degrade]
    Q1 -->|No| Q3{Is it unexpected\nbut not failing?}