Many Envoy components resolve DNS: different cluster types (
the dynamic forward proxy system (which is
composed of a cluster and a filter);
the udp dns filter, etc.
Envoy uses c-ares as a third party DNS resolution library.
On Apple OSes Envoy additionally offers resolution using Apple specific APIs via the
envoy.restart_features.use_apple_api_for_dns_lookups runtime feature.
The Apple-based DNS Resolver emits the following stats rooted in the
dns.apple stats tree:
Number of failed attempts to connect to the DNS server
Number of failed attempts to obtain a file descriptor to the socket to the DNS server
Number of failures when processing data from the DNS server