This should work, but the configuration is a little persnickity.
Can you show us your CoreDNS config? In particular, which IP are you binding to? UDP responses have to come from the fly-global-services IP. That hostname is defined in /etc/hosts. Some libraries that bind to 0.0.0.0 don’t return packets from the right IP, they use the first IP configured on the interface. It’s possible UDP DNS isn’t working for this reason. More details here: UDP reply from unexpected source - #4 by conblem