A fixed OTA_DOWNLOAD_MAX_CONCURRENT=10 throttled a legitimate coordinated rollout even
on a perfectly healthy server, and a shed 503 costs a client a full ~30-min re-check
cycle. Made the download guard's concurrency + rate caps band-aware:
- normal -> serve FREELY (no cap): a whole-fleet rollout isn't staggered when healthy
- elevated -> the configured caps engage (early backpressure)
- critical -> shed 503 (the real protection, unchanged)
Kill switch OTA_DOWNLOAD_GUARD_ENABLED=false disables it entirely.
Tests updated: normal serves 50/50 with 0 shed; caps + shed now asserted under elevated;
storm harness OTA flood runs under elevated (the loaded state). Suite green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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>
