DNS Resolution

Many Envoy components resolve DNS: different cluster types ( strict dns, logical dns); 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.

Envoy provides DNS resolution through extensions, and contains 3 built-in extensions:

1. c-ares: CaresDnsResolverConfig

2. Apple (iOS/macOS only): AppleDnsResolverConfig

3. getaddrinfo: GetAddrInfoDnsResolverConfig

For an example of a built-in DNS typed configuration see the HTTP filter configuration documentation.

The c-ares based DNS Resolver emits the following stats rooted in the dns.cares stats tree:

Name	Type	Description
resolve_total	Count	Number of DNS queries
pending_resolutions	Gauge	Number of pending DNS queries
not_found	Counter	Number of DNS queries that returned NXDOMAIN or NODATA response
timeout	Counter	Number of DNS queries that resulted in timeout
get_addr_failure	Counter	Number of general failures during DNS quries

The Apple-based DNS Resolver emits the following stats rooted in the dns.apple stats tree:

Name	Type	Description
connection_failure	Counter	Number of failed attempts to connect to the DNS server
get_addr_failure	Counter	Number of general failures when calling GetAddrInfo API
network_failure	Counter	Number of failures due to network connectivity
processing_failure	Counter	Number of failures when processing data from the DNS server
socket_failure	Counter	Number of failed attempts to obtain a file descriptor to the socket to the DNS server
timeout	Counter	Number of queries that resulted in a timeout