If your users are inside mainland China, the standard region-routing tricks fall apart. IP geolocation is unreliable behind the Great Firewall, so instead of guessing where a user is, our app races both of its backends and uses whichever responds first. When neither answers, a blocked request to Google becomes the tiebreaker: its fast TCP reset reliably means you're behind the wall. Two bonus lessons: detection should never block app startup, and an over-eager global failover counter can turn on...