# Golden signals expose overload

> For agents: start with the [agent guide](https://ratstack.sh/llms.txt). Every page is Markdown by default; add `Accept: text/html` for HTML.

Free workshop: [Build Agent Loops That Never Stop Shipping](/tokenmaxx#interested).

[Service](/lore/services-capture-dependencies) 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](/lore/durability-bibliography#q18); [B8](/lore/durability-bibliography#b8-monitoring-distributed-systems).

## Failure it prevents

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

## Our Effect 4.0.0 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 check is our proposal. The books do not prescribe it.

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

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

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

## Sources

1. [Ewaschuk, Rob. Monitoring Distributed Systems. O’Reilly, 2016.](https://sre.google/sre-book/monitoring-distributed-systems/)
   O’Reilly. The Four Golden Signals; Black-Box Versus White-Box; Symptoms Versus Causes. Accessed 2026-10-23.

2. [Effect contributors. Effect 4.0.0. Metric.ts](https://github.com/Effect-TS/effect/blob/67ba4e46a11ccda0b6761578bfd22c04ae00167d/packages/effect/src/Metric.ts)
   Effect-TS. Pinned source for our Effect mapping, not a claim from the book. Accessed 2026-10-23.

## Linked from

- Agent guide → An Effect stack so pure (aspirational) Kit Langton will blush. → [Read page](https://ratstack.sh/llms.txt)

- Change log → What changed in the files served here, newest first. → [Read page](https://ratstack.sh/log)

- Dead letters need a return path → Exhausted work needs durable evidence, an owner, and deliberate redrive. → [Read page](https://ratstack.sh/lore/dead-letters-need-a-return-path)

- durability → Keep a rat-stack app standing when a provider, pool, or dependency slows down or a worker dies. Use at any I/O boundary, connection pool, provider call, shared waiter, fan-out, flag, gate, or work that can outlive a request, or when asked "what happens when this is slow", "add a timeout", "make this durable", or "what survives a crash". → [Read page](https://ratstack.sh/skills/durability)

- Durability bibliography → Books, checked short quotations, source limits, and Effect mapping provenance. → [Read page](https://ratstack.sh/lore/durability-bibliography)

- Durability starts with a recovery record → A reading order for storage, replay, worker ownership, overload, and recovery tests. → [Read page](https://ratstack.sh/lore/durability)

- Full agent guide → An Effect stack so pure (aspirational) Kit Langton will blush. → [Read page](https://ratstack.sh/llms-full.txt)

- Rat Stack lore | rat-stack → Short, source-grounded notes on the ideas and decisions behind rat-stack. → [Read page](https://ratstack.sh/lore)

- Source change history (log.md) → The generated change log as Markdown. → [Read page](https://ratstack.sh/log.md)