OmniRoute/docs/architecture/RESILIENCE_GUIDE.md

---
title: "Resilience Guide"
version: 3.8.40
lastUpdated: 2026-06-28
---

# Resilience Guide

OmniRoute has three distinct but related resilience mechanisms. Each has a different scope and purpose. Keep them separate when debugging routing behavior.

![3-layer resilience model](../diagrams/exported/resilience-3layers.svg)

> Source: [diagrams/resilience-3layers.mmd](../diagrams/resilience-3layers.mmd)

## 1. Provider Circuit Breaker

**Scope:** entire provider (e.g., `glm`, `openai`, `anthropic`).

**Purpose:** stop sending traffic to a provider that is repeatedly failing at the upstream/service level.

**Implementation:**

- Core class: `src/shared/utils/circuitBreaker.ts`
- Wiring: `src/sse/handlers/chatHelpers.ts`, `src/sse/handlers/chat.ts`
- Status API: `GET /api/monitoring/health`
- Reset API: `POST /api/resilience/reset`
- Wrappers: `open-sse/services/accountFallback.ts`
- DB table: `domain_circuit_breakers`

**States:**

- `CLOSED` — normal traffic allowed
- `DEGRADED` — traffic still allowed, but elevated provider failures are being tracked
- `OPEN` — provider temporarily blocked; combo routing skips it
- `HALF_OPEN` — reset timeout elapsed; probe request allowed

**Configurable defaults (`open-sse/config/constants.ts`, exposed in Dashboard → Settings → Resilience):**

| Class   | Degraded at | Opens at    | Reset timeout |
| ------- | ----------- | ----------- | ------------- |
| OAuth   | 5 failures  | 8 failures  | 60s           |
| API-key | 7 failures  | 12 failures | 30s           |
| Local   | derived     | 2 failures  | 15s           |

`degradationThreshold` controls when a provider enters `DEGRADED`; `failureThreshold` controls when it opens and is skipped. Local provider profiles are not exposed on the Resilience settings page yet.

**Trip codes:** only provider-level statuses `[408, 500, 502, 503, 504]`. Do NOT trip for account-level errors (most 401/403/429 — those belong to cooldown or lockout).

**Lazy recovery:** when `OPEN` expires, `getStatus()`, `canExecute()`, `getRetryAfterMs()` refresh state to `HALF_OPEN`. No background timer needed.

---

## 2. Connection Cooldown

**Scope:** single provider connection/account/key.

**Purpose:** skip one bad key while other connections for the same provider keep serving.

**Implementation:**

- Mark unavailable: `src/sse/services/auth.ts::markAccountUnavailable()`
- Selection: `getProviderCredentials*` in same file
- Cooldown calc: `open-sse/services/accountFallback.ts::checkFallbackError()`
- Settings: `src/lib/resilience/settings.ts`

**Fields per connection:**

- `rateLimitedUntil` — timestamp until cooldown expires
- `testStatus: "unavailable"`
- `lastError`, `lastErrorType`, `errorCode`
- `backoffLevel` — exponential backoff counter

**Default cooldowns:**

- OAuth base: 5s
- API-key base: 3s
- API-key 429: prefers upstream `Retry-After`/reset headers/parseable reset text
- Backoff: `baseCooldownMs * 2 ** failureIndex`

**Anti-thundering-herd guard:** prevents concurrent failures from over-extending cooldown or double-incrementing `backoffLevel`.

**Terminal states (NOT cooldowns):**

- `banned` — set by banned-keyword / account-ban detection (see [BAN_DETECTION](../security/BAN_DETECTION.md))
- `expired`
- `credits_exhausted`

These persist until credentials change or an operator resets them. Do not overwrite terminal states with transient cooldown state.

**Lazy recovery:** when `rateLimitedUntil` is past, connection becomes eligible again. On successful use, `clearAccountError()` clears all error fields.

### Session affinity (#7274)

**Scope:** one client session (`X-Session-Id` / `x-codex-session-id` / `x-omniroute-session` header) pinned to one connection, for **any** provider.

**Purpose:** keep a multi-turn agent (Claude Code, aider, custom agents) on the same account across requests, reducing cross-account context loss and repeated cold-start 429s on providers with per-account session state.

**Implementation:**

- TTL resolution: `src/sse/services/sessionAffinityPin.ts::resolveSessionAffinityTtlMs()`
- Pin selection/creation: `src/sse/services/sessionAffinityPin.ts::selectSessionAffinityConnection()`
- Header extraction (generic, any provider): `src/sse/services/auth.ts::extractSessionAffinityKey()`
- Persisted pin table: `sessionAccountAffinity` (`src/lib/db/sessionAccountAffinity.ts`)
- Setting: `sessionAffinityTtlMs` (global TTL in ms, `0` disables) — `src/lib/db/settings.ts`. Renamed from the Codex-only `codexSessionAffinityTtlMs` by migration `124_generic_session_affinity_ttl.sql`, which carries over any previously-configured Codex TTL as the new default.

Before #7274, `resolveSessionAffinityTtlMs()` hard-bailed to `0` for every provider except `codex`, so the TTL setting (and the session headers) had no effect anywhere else even though the pinning mechanism and header extraction were already provider-agnostic. The fix removed that early-return; the TTL now applies uniformly to every provider once set globally above `0`.

The three session-affinity headers are never forwarded upstream — executors build their own upstream headers from scratch rather than passing client headers through, so this stays an internal correlation id only.

---

## 3. Model Lockout

**Scope:** provider + connection + model triple.

**Purpose:** avoid disabling a whole connection when only one model is unavailable or quota-limited.

**Examples:**

- Per-model quota providers returning 429
- Local providers returning 404 for one missing model
- Provider-specific mode/model permission failures (e.g., Grok modes)

**Implementation:** `open-sse/services/accountFallback.ts` — `lockModel()`, `clearModelLock()`, `getAllModelLockouts()`.

### Model Cooldowns Dashboard (v3.8.0)

UI: Settings → Model Cooldowns (`src/app/(dashboard)/dashboard/settings/components/ModelCooldownsCard.tsx`)

Lists active lockouts with: provider, connection, model, reason, expiresAt. Operators can manually re-enable a model from the card.

**REST API:**

- `GET /api/resilience/model-cooldowns` — list active lockouts
- `DELETE /api/resilience/model-cooldowns` — manual re-enable. Body: `{provider, connection, model}`. Auth: management.

### Lockout settings UI + success-decay recovery (v3.8.23)

Model lockout went from always-on hardcoded behavior to a fully configurable,
opt-in feature with its own settings card and a self-healing recovery path.

**Settings card:** Settings → Model Lockout
(`src/app/(dashboard)/dashboard/settings/components/ModelLockoutCard.tsx`).
This is **distinct** from the read-only `ModelCooldownsCard` above (which only
_lists_ active lockouts) — the new card _configures the parameters_. Defaults
live in `DEFAULT_MODEL_LOCKOUT_SETTINGS`
(`src/lib/resilience/modelLockoutSettings.ts`):

| Setting                 | Default                          | Meaning                                                        |
| ----------------------- | -------------------------------- | -------------------------------------------------------------- |
| `enabled`               | `false`                          | Master toggle — model lockout is **off by default**.           |
| `errorCodes`            | `[403, 404, 429, 502, 503, 504]` | Upstream statuses that count as a model-scoped failure.        |
| `baseCooldownMs`        | `120_000` (120 s)                | Initial lockout duration for the first failure.                |
| `maxCooldownMs`         | `1_800_000` (30 min)             | Cap on the escalated cooldown.                                 |
| `maxBackoffSteps`       | `10`                             | Max exponential-backoff escalation steps.                      |
| `useExponentialBackoff` | `true`                           | Whether repeated failures escalate the cooldown exponentially. |

Settings persist through the normal settings store and validate via the
resilience settings schema; the card clamps `baseCooldownMs`/`maxCooldownMs`
(with `maxCooldownMs ≥ baseCooldownMs`) and `maxBackoffSteps`.

**Success-decay recovery:** recovery is **not** purely timer expiry. A healthy
response walks the model's failure count back down so a model that recovered
mid-window stops escalating (and clears) before its timer would. On a successful
combo target, `open-sse/services/combo.ts` calls `decayModelFailureCount()`
(`open-sse/services/accountFallback.ts`), which **halves** the stored
`failureCount` (`Math.floor(failureCount / 2)`); when it reaches `0` the lockout
entry is deleted entirely. The counterpart `recordModelLockoutFailure()`
increments the count (and escalates the cooldown) on failures within the
escalation window. This success-decay is in addition to plain timer expiry —
either path can re-enable a model.

**State:** lockouts are held **in-memory** (per-process `Map`s of
`ModelLockoutEntry` keyed by `provider:connectionId:model`), not persisted to
the DB — they are lost on restart. The _settings_ are persisted; the active
lockout _state_ is ephemeral.

---

## 4. Quota-Share Concurrency Control (v3.8.36)

Subscription accounts (GLM, MiniMax, etc.) often accept only ~1–3 concurrent
requests; exceeding that triggers 429s and cooldowns. This is acute under
**quota-share** (`qtSd/…`) combos, where several API keys share one upstream
account. Three layers keep a shared account from being flooded.

### Per-connection concurrency cap (`max_concurrent`)

Each provider connection can declare a `max_concurrent` ceiling
(`provider_connections.max_concurrent`, set in the connection modal / API / DB).
Leave it empty for no limit. This is the single knob that drives the serialization
layer below — set it to the account's real concurrency (e.g. GLM ~1, MiniMax ~2).

### Quota-share request serialization

When a quota-share dispatch targets a connection that declares a positive
`max_concurrent`, concurrent requests to that **account** are serialized through a
per-connection semaphore (key `qsconn:<connectionId>`): excess requests **wait in
the queue** instead of flooding the account. It is **fail-open** — a saturated
queue or timeout proceeds without a slot rather than ever rejecting a dispatchable
request. Toggle in **Settings → Resilience → Quota-share per-connection
concurrency** (`resilienceSettings.quotaShareConcurrencyLimit.enabled`, default
on). Without a `max_concurrent` cap the behavior is unchanged.

> The quota-share routing gate (`selectQuotaShareTarget`, DRR + P2C) is itself
> fail-open and only _deprioritizes_ an at-cap connection — with a
> single-connection pool it cannot hard-limit, so this semaphore is what actually
> contains the flood.

### Combo cooldown-aware retry

For quota-share and `auto` combos, a request that would crystallize a 429 for a
SHORT transient cooldown waits it out and re-dispatches instead of returning
the 429 — this covers Gemini-class TPM/RPM windows (~60s retry-after) on a
multi-model `auto` combo, e.g. both targets of a 2-model combo hitting a
per-model rate limit. Bounded by `comboCooldownWait` (`enabled`, `maxWaitMs`
65s, `maxAttempts` 2, `budgetMs` 130s, hard ceiling 90s) in **Settings →
Resilience**. It never waits on `quota_exhausted` (locked until midnight) or
auth/not-found reasons.

---

## 5. Request Queue Admission Control (v3.8.49 · issue #6593)

**Scope**: the local per-provider+connection rate-limit queue (`open-sse/services/rateLimitManager.ts`,
backed by Bottleneck), one layer below the three mechanisms above.

**`maxWaitMs` default lowered 120s → 15s.** `resilienceSettings.requestQueue.maxWaitMs`
bounds how long a request may wait in the local queue before it is dropped
(`code: "RATE_LIMIT_QUEUE_TIMEOUT"`, #4165). The factory default fell from 120000ms to
15000ms so a saturated queue fails fast instead of holding a caller for two
minutes; override via `RATE_LIMIT_MAX_WAIT_MS` (env) or the dashboard
(**Settings → Resilience**, 1–30000ms UI ceiling).

**`maxQueueDepth` — opt-in admission cap (new).** `resilienceSettings.requestQueue.maxQueueDepth`
bounds how many requests may sit queued (not yet dispatched) for one
provider+connection at once. When the queue already holds `maxQueueDepth`
requests, a new request is fast-rejected with a typed
`code: "RATE_LIMIT_QUEUE_FULL"` error **before** it ever reaches `limiter.schedule()`
— so the rejection is cheap and happens ahead of any downstream
prompt-compression / translation work for that request. Default `0` =
disabled, preserving the existing unbounded-queue behavior; bounded 0–100000.
Override via `RATE_LIMIT_MAX_QUEUE_DEPTH` (env) or
`resilienceSettings.requestQueue.maxQueueDepth` (dashboard/API patch).

The admission check itself is a pure function
(`open-sse/services/rateLimitManager/admission.ts::checkQueueAdmission`) so
it is unit-testable without a real Bottleneck limiter.

> The RFC that opened #6593 also proposed a `bypassCompressionOnRateLimit`
> flag. This repo's `open-sse/services/compression/` pipeline is
> prompt/context compression on the outbound LLM request (`chatCore.ts`,
> around the `resolveCompressionSettings`/`selectCompressionStrategy` block),
> not HTTP response compression on synthesized 429 bodies — there is no
> matching code path for a literal bypass flag. That prompt-compression step
> also currently runs *before* `withRateLimit()` in the request pipeline, so
> reordering to skip it on a queue-full rejection is a separate, larger
> change than this issue's scope; it was intentionally **not** implemented
> here and is left as a follow-up if the CPU-saving win is worth the
> reordering risk.

---

## Other Resilience Features

- **18 routing strategies** (priority, weighted, round-robin, context-relay, fill-first, p2c, random, least-used, cost-optimized, reset-aware, reset-window, headroom, strict-random, auto, lkgp, context-optimized, fusion, pipeline) — see [AUTO-COMBO.md](../routing/AUTO-COMBO.md).
- **Reset-aware routing** (v3.8.0) — prioritizes connections by quota reset time.
- **Background mode degradation** — Responses API `background: true` degraded to sync with warning.
- **Dynamic tool limit detection** — backs off providers when tool count limits hit.
- **Emergency fallback** — controlled by `OMNIROUTE_EMERGENCY_FALLBACK`; operators can override it from the Feature Flags page without a restart.

---

## Debugging

- All keys for a provider skipped → check both circuit breaker state AND each connection's `rateLimitedUntil`/`testStatus`.
- Provider permanently excluded after reset window → code reading raw `state` instead of `getStatus()`/`canExecute()`.
- One key fails, others should work → prefer connection cooldown over circuit breaker.
- Only one model fails → prefer model lockout over connection cooldown.
- State should self-recover but doesn't → check for future timestamp + read path that refreshes expired state. Permanent statuses require manual changes.

---

## TLS Fingerprinting & Stealth

Provider-specific stealth (JA3/JA4, CCH, obfuscation) is separately documented — see [STEALTH_GUIDE.md](../security/STEALTH_GUIDE.md).

---

## Resilience testing (Phase 8 · Block C)

Beyond unit tests for resilience logic, three tests exercise the runtime under
real stress/failure conditions (all integration/nightly — none block PRs):

| Test        | What                                                                                                                                                                          | Run                                      |
| ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------- |
| Chaos       | Fake-upstream node injects real latency/reset/timeout/503; validates that the circuit breaker opens/recovers and `checkFallbackError` classifies 503 as recoverable fallback. | `RUN_CHAOS_INT=1 npm run test:chaos`     |
| Heap-growth | ~500 streams per `createSSEStream` under `--expose-gc`; fails if the heap grows beyond the ceiling (OOM guard #3069).                                                         | `npm run test:heap`                      |
| k6 soak     | Sustained load against `/api/monitoring/health`; p95/error thresholds.                                                                                                        | `k6 run tests/load/k6-soak.js` (nightly) |

Orchestrated by `.github/workflows/nightly-resilience.yml` (cron + dispatch). In the
default `test:integration`, chaos and heap self-skip (without `RUN_CHAOS_INT`/`--expose-gc`).

---

## See Also

- [Architecture Guide](./ARCHITECTURE.md) — System architecture and internals
- [User Guide](../guides/USER_GUIDE.md) — Providers, combos, CLI integration
- [Auto-Combo Engine](../routing/AUTO-COMBO.md) — 12-factor scoring, mode packs