# Golden signals expose overload

Principle `golden-signals-expose-overload`. Measure latency, traffic, errors, and saturation, including failed work.

Also searched as: four golden signals, black-box monitoring, white-box monitoring.

Service monitoring needs all four golden signals. Separate symptom detection from internal diagnosis, and distinguish failed-request latency from successful latency.

> The four golden signals of monitoring are latency, traffic, errors, and saturation.

Source: [Q18](/bibliography#q18); [B8](/bibliography#b8-monitoring-distributed-systems).

## Failure it prevents

A service reports fast responses while errors rise or scarce capacity is exhausted.

## Our Effect 4.0.5 reading

Metric.counter, gauge, and histogram supply instruments. Connect backlog and parked-work observations through the actual adapters. Define alerts and response outside these constructors.

Source: `packages/effect/src/Metric.ts`.

## How to check

Create a slow dependency and a parked item. Verify that user-visible failure and resource saturation are observable. This is our proposed verification, not a quoted procedure.

Continue with [Dead letters need a return path](/principles/dead-letters-need-a-return-path), [Admission control protects recovery](/principles/admission-controls-new-work).

Connect this to [the existing rat-stack guidance](https://ratstack.sh/lore/concurrent-work-needs-an-owner).

Use [the durability skill](/skills/durability) for the full review. Return to [the durability index](/principles/durability).

## Skills
- [Durability starts with a recovery record](/principles/durability)

## Sources
- Ewaschuk, Rob. *Monitoring Distributed Systems*. O’Reilly, 2016. [Link](https://sre.google/sre-book/monitoring-distributed-systems/). ([b8-monitoring-distributed-systems](/bibliography#b8-monitoring-distributed-systems))

## References
- [Effect contributors. Effect 4.0.5. Metric.ts](https://github.com/Effect-TS/effect/blob/7f524e25cfb49a71ac39b0f44278d08d40dda5de/packages/effect/src/Metric.ts). Pinned source for our Effect mapping, not a claim from the book.