dns: add dns resolver implementation based on Apple APIs (#13074)

Signed-off-by: Jose Nino <jnino@lyft.com>

Mirrored from https://github.com/envoyproxy/envoy @ d3ecdef920c616a3ebc935c19e8e34f71a18d1b6

envoy/api/v2/cluster.proto

@@ -677,10 +677,16 @@ message Cluster {
   // :ref:`STRICT_DNS<envoy_api_enum_value_Cluster.DiscoveryType.STRICT_DNS>`
   // and :ref:`LOGICAL_DNS<envoy_api_enum_value_Cluster.DiscoveryType.LOGICAL_DNS>`
   // this setting is ignored.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple's API only allows overriding DNS resolvers via system settings.
   repeated core.Address dns_resolvers = 18;
 
   // [#next-major-version: Reconcile DNS options in a single message.]
   // Always use TCP queries instead of UDP queries for DNS lookups.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple' API only uses UDP for DNS resolution.
   bool use_tcp_for_dns_lookups = 45;
 
   // If specified, outlier detection will be enabled for this upstream cluster.

envoy/config/bootstrap/v2/bootstrap.proto

@@ -169,6 +169,9 @@ message Bootstrap {
   // when :ref:`dns_resolvers <envoy_api_field_Cluster.dns_resolvers>` and
   // :ref:`use_tcp_for_dns_lookups <envoy_api_field_Cluster.use_tcp_for_dns_lookups>` are
   // specified.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple' API only uses UDP for DNS resolution.
   bool use_tcp_for_dns_lookups = 20;
 }
 

envoy/config/bootstrap/v3/bootstrap.proto

@@ -234,6 +234,9 @@ message Bootstrap {
   // when :ref:`dns_resolvers <envoy_api_field_config.cluster.v3.Cluster.dns_resolvers>` and
   // :ref:`use_tcp_for_dns_lookups <envoy_api_field_config.cluster.v3.Cluster.use_tcp_for_dns_lookups>` are
   // specified.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple' API only uses UDP for DNS resolution.
   bool use_tcp_for_dns_lookups = 20;
 
   // Specifies optional bootstrap extensions to be instantiated at startup time.

envoy/config/bootstrap/v4alpha/bootstrap.proto

@@ -220,6 +220,9 @@ message Bootstrap {
   // when :ref:`dns_resolvers <envoy_api_field_config.cluster.v4alpha.Cluster.dns_resolvers>` and
   // :ref:`use_tcp_for_dns_lookups <envoy_api_field_config.cluster.v4alpha.Cluster.use_tcp_for_dns_lookups>` are
   // specified.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple' API only uses UDP for DNS resolution.
   bool use_tcp_for_dns_lookups = 20;
 
   // Specifies optional bootstrap extensions to be instantiated at startup time.

envoy/config/cluster/v3/cluster.proto

@@ -829,10 +829,16 @@ message Cluster {
   // :ref:`STRICT_DNS<envoy_api_enum_value_config.cluster.v3.Cluster.DiscoveryType.STRICT_DNS>`
   // and :ref:`LOGICAL_DNS<envoy_api_enum_value_config.cluster.v3.Cluster.DiscoveryType.LOGICAL_DNS>`
   // this setting is ignored.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple's API only allows overriding DNS resolvers via system settings.
   repeated core.v3.Address dns_resolvers = 18;
 
   // [#next-major-version: Reconcile DNS options in a single message.]
   // Always use TCP queries instead of UDP queries for DNS lookups.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple' API only uses UDP for DNS resolution.
   bool use_tcp_for_dns_lookups = 45;
 
   // If specified, outlier detection will be enabled for this upstream cluster.

envoy/config/cluster/v4alpha/cluster.proto

@@ -839,10 +839,16 @@ message Cluster {
   // :ref:`STRICT_DNS<envoy_api_enum_value_config.cluster.v4alpha.Cluster.DiscoveryType.STRICT_DNS>`
   // and :ref:`LOGICAL_DNS<envoy_api_enum_value_config.cluster.v4alpha.Cluster.DiscoveryType.LOGICAL_DNS>`
   // this setting is ignored.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple's API only allows overriding DNS resolvers via system settings.
   repeated core.v4alpha.Address dns_resolvers = 18;
 
   // [#next-major-version: Reconcile DNS options in a single message.]
   // Always use TCP queries instead of UDP queries for DNS lookups.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple' API only uses UDP for DNS resolution.
   bool use_tcp_for_dns_lookups = 45;
 
   // If specified, outlier detection will be enabled for this upstream cluster.

envoy/extensions/common/dynamic_forward_proxy/v3/dns_cache.proto

@@ -98,5 +98,8 @@ message DnsCacheConfig {
 
   // [#next-major-version: Reconcile DNS options in a single message.]
   // Always use TCP queries instead of UDP queries for DNS lookups.
+  // Setting this value causes failure if the
+  // ``envoy.restart_features.use_apple_api_for_dns_lookups`` runtime value is true during
+  // server startup. Apple' API only uses UDP for DNS resolution.
   bool use_tcp_for_dns_lookups = 8;
 }