Metrics & the three-pillars model

Logs tell you about individual events; metrics tell you about aggregates over time — how many requests, how full the queue, how slow the p99 — the time the slowest one percent of requests take. Metrics are the cheap, always-on numbers you dashboard and alert on. This module builds a metrics registry and places it in the "three pillars" model: logs, metrics, traces.

Metrics tell you that a request was slow. The last module adds the third pillar — tracing — which tells you which stage was slow.