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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