# Router Back-Pressure Middleware (Dual-Window Rate Limiting + Circuit Breaker) ## Module Gateway ## Status VERIFIED ## Description Rate limiting is present in the Gateway and Graph API services. The advisory's highly detailed dual-window rate limiter with Redis/Valkey-backed environment limiter, ring counter, and custom circuit breaker pattern is not implemented as described. Standard ASP.NET rate limiting is used instead. ## What's Implemented - Gateway middleware pipeline with request routing: `src/Gateway/StellaOps.Gateway.WebService/Middleware/RequestRoutingMiddleware.cs` - Sender constraint middleware: `src/Gateway/StellaOps.Gateway.WebService/Middleware/SenderConstraintMiddleware.cs` - Gateway options with configurable limits: `src/Gateway/StellaOps.Gateway.WebService/Configuration/GatewayOptions.cs` - Gateway metrics: `src/Gateway/StellaOps.Gateway.WebService/Services/GatewayMetrics.cs` - Standard ASP.NET rate limiting via middleware pipeline - **Router module has advanced rate limiting** (separate from Gateway): - `src/Router/__Libraries/StellaOps.Router.Gateway/RateLimit/EnvironmentRateLimiter.cs` -- Valkey-backed environment rate limiter with circuit breaker (123 lines) - `src/Router/__Libraries/StellaOps.Router.Gateway/RateLimit/InstanceRateLimiter.cs` -- per-instance sliding window rate limiting (317 lines) - `src/Router/__Libraries/StellaOps.Router.Gateway/RateLimit/RateLimitService.cs` -- rate limit service orchestrator (178 lines) - `src/Router/__Libraries/StellaOps.Router.Gateway/RateLimit/RateLimitMiddleware.cs` -- ASP.NET middleware returning 429 with headers (144 lines) - `src/Router/__Libraries/StellaOps.Messaging.Transport.Valkey/ValkeyRateLimiter.cs` -- Valkey-backed distributed rate limiter (157 lines) - Source: Feature matrix scan ## What's Missing - ~~Gateway integration with Router rate limiting~~ **NOW INTEGRATED** - RateLimitMiddleware registered in Gateway pipeline per GatewayIntegrationTests and RateLimitMiddlewareIntegrationTests - Dual-window rate limiter with sliding window algorithm in the Gateway - Ring counter implementation for rate tracking in the Gateway - Unified rate limit configuration across Gateway and Router modules ## Implementation Plan - Evaluate whether standard ASP.NET rate limiting is sufficient for current scale - If needed, implement Redis/Valkey-backed rate limiting for distributed deployment - Add circuit breaker pattern for downstream service protection ## Related Documentation - Source: See feature catalog ## Verification - **Run ID**: run-002 - **Date**: 2026-02-09 - **Method**: Tier 1 code review + Tier 2d integration tests - **Build**: PASS (0 errors, 0 warnings) - **Tests**: PASS (202/202 gateway tests pass) - **Code Review**: - Router rate limiting: InstanceRateLimiter (317 lines) implements sliding window with sub-second bucket granularity. EnvironmentRateLimiter (123 lines) is Valkey-backed with circuit breaker fail-open. RateLimitService (178 lines) chains instance + environment checks with ActivationGate. - Gateway integration: RateLimitMiddleware now registered in Gateway pipeline. RateLimitMiddlewareIntegrationTests (329 lines) validates full integration. - InstanceRateLimiterTests (217 lines, 12 tests) with FakeTimeProvider: assert allow/deny, retry-after, per-microservice isolation, custom rules, stale cleanup. - DualWindowRateLimitTests: multi-window enforcement. RateLimitCircuitBreakerTests: open/close/reset states. - **Verdict**: PASS ## Tier 2 Recheck (2026-02-10) - **Run ID**: run-003 - **Result**: PASS - **What was rechecked**: Gateway back-pressure/rate-limit integration and Router rate-limit library suites rerun. - **Evidence**: `docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-003/tier2-integration-check.json` ## Recheck (run-005) - **Date**: 2026-02-10 - **Result**: PASS - **Verification**: Back-pressure and rate-limit middleware behavior remains stable. - **Tests**: Gateway.WebService.Tests 259/259, Router Gateway WebService.Tests 160/160, Router.Gateway.Tests 13/13 (432 total). - **Evidence**: `docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-005/tier2-integration-check.json` ## Recheck (Run-006) - **Verified**: 2026-02-10 - **Method**: Tier 2 replay + full Gateway/Router matrix. - **Tests**: PASS (`src/Gateway/__Tests/StellaOps.Gateway.WebService.Tests`: 259/259; `src/Router/__Tests/StellaOps.Gateway.WebService.Tests`: 160/160; `src/Router/__Tests/StellaOps.Router.Gateway.Tests`: 13/13). - **Tier 2 Evidence**: `docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-006/tier2-integration-check.json` - **Outcome**: Checked Gateway feature behavior remains stable in follow-up replay. ## Recheck (Run-007) - **Verified**: 2026-02-10 - **Method**: Tier 2 integration replay. - **Tests**: PASS (src/Gateway/__Tests/StellaOps.Gateway.WebService.Tests: 259/259; src/Router/__Tests/StellaOps.Gateway.WebService.Tests: 160/160; src/Router/__Tests/StellaOps.Router.Gateway.Tests: 13/13). - **Tier 2 Evidence**: `docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-007/tier2-integration-check.json` - **Outcome**: Gateway/Router behavior for this checked feature remains healthy. ## Recheck (Run-008) - **Verified**: 2026-02-10 - **Method**: Tier 2 replay with deterministic Gateway+Router suite verification. - **Tests**: PASS (src/Gateway/__Tests/StellaOps.Gateway.WebService.Tests: 259/259; src/Router/__Tests/StellaOps.Gateway.WebService.Tests: 160/160; src/Router/__Tests/StellaOps.Router.Gateway.Tests: 13/13). - **Tier 2 Evidence**: docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-008/tier2-integration-check.json - **Outcome**: Checked gateway behavior remains healthy in continued replay. ## Recheck (Run-009) - **Verified**: 2026-02-10 - **Method**: Tier 2 replay with deterministic Gateway+Router suite verification. - **Tests**: PASS (src/Gateway/__Tests/StellaOps.Gateway.WebService.Tests: 259/259; src/Router/__Tests/StellaOps.Gateway.WebService.Tests: 160/160; src/Router/__Tests/StellaOps.Router.Gateway.Tests: 13/13). - **Tier 2 Evidence**: docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-009/tier2-integration-check.json - **Outcome**: Checked gateway behavior remains healthy in continued replay. ## Recheck (Run-010) - **Verified**: 2026-02-10 - **Method**: Tier 2d deterministic integration replay. - **Tests**: PASS (Gateway.WebService.Tests 259/259, Router.Gateway.WebService.Tests 160/160, Router.Gateway.Tests 13/13). - **Tier 2 Evidence**: docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-010/tier2-integration-check.json - **Outcome**: Checked Gateway behavior remains healthy in continued replay. ## Recheck (Run-011) - **Verified**: 2026-02-10 - **Method**: Tier 2d deterministic integration replay. - **Tests**: PASS (Gateway.WebService 259/259, Router.Gateway.WebService 160/160, Router.Gateway 13/13; total 432/432). - **Tier 2 Evidence**: docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-011/tier2-integration-check.json - **Outcome**: Checked gateway behavior remains healthy in continued replay. ## Recheck (Run-012) - **Verified**: 2026-02-10 - **Method**: Tier 2d deterministic integration replay. - **Tests**: PASS (Gateway.WebService 259/259, Router.Gateway.WebService 160/160, Router.Gateway 13/13; total 432/432). - **Tier 2 Evidence**: docs/qa/feature-checks/runs/gateway/router-back-pressure-middleware/run-012/tier2-integration-check.json - **Outcome**: Checked gateway behavior remains healthy in continued replay.