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RED & USE Methods
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1 min
Table of Contents
🟠P1 — systematic approaches to choosing what to measure
RED Method (for request-driven services) #
| Signal | Metric | Alert when… |
|---|---|---|
| R ate | Requests per second | Drops below baseline |
| E rror | Error rate (% of requests) | Exceeds threshold (e.g. >1%) |
| D uration | Request latency (p50, p95, p99) | p99 exceeds SLO (e.g. >500ms) |
USE Method (for infrastructure resources) #
| Signal | Metric | Alert when… |
|---|---|---|
| U tilisation | % of resource capacity used | >80% sustained |
| S aturation | Queue depth / backlog | Growing steadily |
| E rrors | Hardware/resource errors | Any occurrence |
Instinct #
RED for services, USE for infrastructure.
In a design interview, after sketching the architecture:
For each service, I’d instrument RED metrics. For the database and cache layers, USE metrics. Alerting on error rate >1% and p99 latency >SLO.
References #
- The RED Method — Tom Wilkie (originator)
- The USE Method — Brendan Gregg (originator)
- Google SRE: Monitoring Distributed Systems — the “four golden signals”