The fleet SNATs to one IP, so nothing on the OTA path may key on IP.
- /api/update/check: EARLY-RETURN before any filesystem call when the breaker won't
offer (rate-backoff / up-to-date / phantom / client-newer). A looping client that
gets rate-backoff now does ZERO fs — the flood can't become a statSync flood.
- lib/apk-cache.js: resolve APK path/size/mtime once at boot + refresh on an interval;
the check/download endpoints read cached metadata (get() does no fs, proven by test).
- lib/ota-download-guard.js + /download/apk: GLOBAL concurrency + rate caps + critical-
band shed (503 Retry-After), NEVER per-IP. Replaces the per-IP-per-10min log throttle
(which hid the flood under SNAT) with a per-window served/shed aggregate so a download
flood is VISIBLE. Bounded single rolling-state object; in-flight released on finish/close.
- Breaker unchanged; no IP limiting or device_id requirement added (legacy field clients
send no device_id on OTA checks — must keep working).
Tests: apk-cache get() = 0 statSync over 1000 reads; download guard sheds past global
concurrency + per-window rate + critical band; admit() has no IP parameter. Suite 259/259.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
