CoreDNS at 10.43.0.10 returns SERVFAIL for demo.flow-master.ai in
this environment. Including it in the resolver list caused nginx
to query it first, get SERVFAIL, and return 502 before falling
back to 1.1.1.1. Pinning to public resolvers eliminates the cold
miss. 300s TTL caches the result.
Restored $variable form for proxy_pass because the static-hostname
form failed pod readiness (DNS query at config-load time hits
the same SERVFAIL).
The previous $variable form forced lazy per-request DNS resolution.
Per-request lookups against 10.43.0.10 → SERVFAIL → cold-cache 502
even when downstream was healthy. Switching to a literal hostname
makes nginx resolve once at startup and reuse the cached upstream IP
for the lifetime of the worker. Cloudflare anycast is stable so this
is safe.
canvas-bot