Observability

If you cannot ask arbitrary questions about your system's behavior from the outside, your system is not observable — it is merely monitored.

Observability is the ability to understand internal system state from its external outputs. Three complementary signals make this possible: logs (discrete events), metrics (aggregate measurements), and traces (request-scoped causal chains). Each pillar answers different questions. Using the wrong pillar for a question wastes resources and hides the answer.

This skill covers high-level observability discipline — purposes, interconnection, and good practices for all three pillars. It is technology-agnostic: specific tools (Prometheus, StatsD, OpenTelemetry) have their own dedicated skills.

The Three Pillars