> Old server nginx converted to reverse proxy We wrote a Python script that parsed every server {} block across all 34 Nginx site configs, backed up the originals, and replaced them with proxy configurations pointing to the new server. This meant that during DNS propagation, any request still hitting the old IP was silently forwarded. No user would see a disruption.

What was the config on the receiving side to support this? Did you whitelist the old server IP to trust the forwarding headers? Otherwise you’d get the old server IP in your app logs. Not a huge deal for an hour but if something went wrong it can get confusing.