feat: add redis_decay backend and soft-breach response header - #1214
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feat: add redis_decay backend and soft-breach response header#1214ysolomon-plat wants to merge 1 commit into
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Adds BACKEND_TYPE=redis_decay: a continuously-decaying counter (GCRA family) executed as an atomic Redis EVAL. Unlike the fixed-window redis backend, cache keys carry no window timestamp, so budgets never reset at a boundary and the 2x boundary-burst is impossible by construction. Honors per-descriptor hits_addend. Fail-open on Redis errors. Cluster-safe: EVAL routes by cache key. Also adds SOFT_BREACH_HEADER_RATIO: when set (0..1), admitted requests whose remaining budget falls inside the soft band get an x-ratelimit-soft-breach: 1 response header, so clients can degrade before hard 429s. Computed generically from CurrentLimit/LimitRemaining, so it works with any cache backend. Covered by test/redis_decay (real EVAL execution on miniredis: boundary immunity, decay recovery, flood behavior, corrupt data, backward clock, fail-open, hits_addend) and test/service/soft_breach_test.go. All existing tests pass. Load-tested on Istio 1.30 / Gateway API: 3,950 rps sustained on one replica, +2.3ms p50 overhead, exact admission under concurrency. Refs envoyproxy#32 (rolling window request, open since 2018).
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Superseded by #1215 (same change, rebuilt with DCO sign-off and cleaned-up comments). |
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Adds BACKEND_TYPE=redis_decay: a continuously-decaying counter (GCRA family) executed as an atomic Redis EVAL. Unlike the fixed-window redis backend, cache keys carry no window timestamp, so budgets never reset at a boundary and the 2x boundary-burst is impossible by construction. Honors per-descriptor hits_addend. Fail-open on Redis errors. Cluster-safe: EVAL routes by cache key.
Also adds SOFT_BREACH_HEADER_RATIO: when set (0..1), admitted requests whose remaining budget falls inside the soft band get an x-ratelimit-soft-breach: 1 response header, so clients can degrade before hard 429s. Computed generically from CurrentLimit/LimitRemaining, so it works with any cache backend.
Covered by test/redis_decay (real EVAL execution on miniredis: boundary immunity, decay recovery, flood behavior, corrupt data, backward clock, fail-open, hits_addend) and test/service/soft_breach_test.go. All existing tests pass.
Load-tested on Istio 1.30 / Gateway API: 3,950 rps sustained on one replica, +2.3ms p50 overhead, exact admission under concurrency.
Refs #32 (rolling window request, open since 2018).