WIP: Add concurrent request rate limiter and optimize middleware stack - #5361
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serdarozerr wants to merge 10 commits into
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… done. Introduces ConcurrencyRateLimiter middleware to limit concurrent requests per user across all endpoints. Supports separate logging and blocking thresholds for smooth rollout, Redis and in-memory store backends, thread-safe singleton limiter instance, and RetryAfter header estimation based on request duration. Disabled by default via config. Also separates user DB lookup from token decoding into a dedicated UserContextSetter middleware, and moves RequestMetrics after rate limiters in the middleware stack.
…cs and RequestLogs preserved
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philippthun
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Sep 11, 2026
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| module VCAP::CloudController | ||
| class RackAppBuilder | ||
| # rubocop:disable Metrics/MethodLength, Metrics/BlockLength |
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Maybe you could refactor this in order to reduce the method length...
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Refactoring is possible but would require removing the builder block and introducing extra methods, which might hurts readability. So i thought better to keep current form since the full middleware stack is visible in order in one place.
stephanme
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Sep 15, 2026
- implementation on #5361 was improved and reaches more throughput now - all measurements run for 300s - more detailed explanation how to determine max throughput - some more arguments for replacing nginx by a dedicated CAPI router
- Introduce ConcurrentRequestCounter with InMemoryStore and RedisStore backends using atomic Lua scripts for check-and-increment; rejected requests do not increment the counter (no phantom count) - Add ConcurrencyRateLimiter and ServiceBrokerRateLimiter middlewares backed by the new counter - Extract UserId, InternalOrRootApi, TooManyRequests, BasicAuth mixins - Derive redis_connection_pool_size and redis_counter_ttl_seconds from puma max_threads and request_timeout_in_seconds in config - Add unit tests for all new components
serdarozerr
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Summary
Concurrent request rate limiter: Introduced
ConcurrencyRateLimitermiddleware that limits the number of concurrent in-flight requests per user (or IP for unauthenticated requests). Supports separatelogging_limit(warn only) andblocking_limit(return 429) for smooth rollout. Disabled by default via config. Backed by Redis (with TTL-based safety cleanup) or in-memory store for single-process deployments. Admins are rate limited the same as regular users.Middleware stack optimization: Split
SecurityContextSetterinto two concerns — token decoding only (configure_token_only) happens early in the stack, and user DB lookup (configure_user) is deferred to a newUserContextSettermiddleware placed after rate limiters. This means rate limiting never triggers a DB lookup for blocked requests.RequestMetricsis also moved after rate limiters so that blocked 429 responses are excluded from request metrics, keeping metrics focused on requests that actually reached the application.Changes
middleware/concurrency_rate_limiter.rb— new middleware withConcurrencyRateLimiter,ConcurrencyLimiter,ConcurrentRedisStore,ConcurrentInMemoryStoremiddleware/user_context_setter.rb— new middleware for deferred user DB lookupmiddleware/security_context_setter.rb— now callsconfigure_token_onlyinstead of fullconfigurelib/cloud_controller/security/security_context_configurer.rb— addedconfigure_token_onlyandconfigure_usermethodslib/cloud_controller/rack_app_builder.rb— wired new middlewares, movedRequestMetricsafter rate limiterslib/cloud_controller/config_schemas/api_schema.rb— addedconcurrency_rate_limiterconfig schemaRetry-Afterheader added on 429 responses from the concurrent rate limiter.Related PRs
Concurrency ratelimiter specs capi-release#679
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