# Admission control protects recovery

> 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).

A busy [service](/lore/services-capture-dependencies) needs a way to reject incoming work. Callers must respect its signal instead of immediately amplifying the same overload.

Book basis: [B4](/lore/durability-bibliography#b4-release-it), [B12](/lore/durability-bibliography#b12-site-reliability-engineering).

## Failure it prevents

An overloaded service keeps accepting work and extends its own outage.

## Our Effect 4.0.0 reading

`Queue` and `Semaphore` offer local capacity controls. They do not choose the ingress response or implement caller cooperation. Model overload modes explicitly when needed.

Source: `packages/effect/src/Queue.ts`, `packages/effect/src/Semaphore.ts`.

## How to check

Exceed capacity. Observe a truthful refusal or durable deferral, bounded backlog, and recovery after demand falls. This check is our proposal. The books do not prescribe it.

Continue with [Retry load needs a budget](/lore/retry-load-needs-a-budget), [Backpressure reaches the producer](/lore/backpressure-reaches-the-producer).

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. [Nygard, Michael T. Release It!: Design and Deploy Production-Ready Software. Pragmatic Bookshelf, 2007.](https://archive.org/details/releaseitdesignd0000nyga)
   Pragmatic Bookshelf. §4.4 Unbounded Result Sets; Chapter 5 Stability Patterns: §5.1 Timeouts, §5.2 Circuit Breaker, §5.3 Bulkheads, §5.4 Steady State, §5.5 Fail Fast, §5.6 Handshaking, §5.7 Test Harness, §5.8 Decoupling Middleware. Accessed 2026-10-23.

2. [Beyer, Betsy; Jones, Chris; Petoff, Jennifer; Murphy, Niall Richard, editors. Site Reliability Engineering: How Google Runs Production Systems. O’Reilly, 2016.](https://sre.google/sre-book/table-of-contents/)
   O’Reilly. Chapter 3 Embracing Risk; Chapter 22 Addressing Cascading Failures (Mike Ulrich); Chapter 26 General Principles of SRE as Applied to Data Integrity; Chapter 27 Reliable Product Launches at Scale. Section-only excerpts limit detailed attribution. Accessed 2026-10-23.

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

4. [Effect contributors. Effect 4.0.0. Semaphore.ts](https://github.com/Effect-TS/effect/blob/67ba4e46a11ccda0b6761578bfd22c04ae00167d/packages/effect/src/Semaphore.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)

- Backpressure reaches the producer → Bounded consumption helps only when upstream respects waiting or refusal. → [Read page](https://ratstack.sh/lore/backpressure-reaches-the-producer)

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

- 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)

- Golden signals expose overload → Measure latency, traffic, errors, and saturation, including failed work. → [Read page](https://ratstack.sh/lore/golden-signals-expose-overload)

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

- Retry load needs a budget → One retry owner must control attempts, delay, and aggregate load. → [Read page](https://ratstack.sh/lore/retry-load-needs-a-budget)

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