fix(grpc): default to native dns resolver on macos (#1125)

* fix: address mac dns resolver issue

Signed-off-by: Samantha Coyle <sam@diagrid.io>

* fix: scope down to grpc client helpers

Signed-off-by: Samantha Coyle <sam@diagrid.io>

---------

Signed-off-by: Samantha Coyle <sam@diagrid.io>

Author: sicoyle

dapr/aio/clients/grpc/client.py

@@ -57,6 +57,7 @@
     MetadataTuple,
     convert_dict_to_grpc_dict_of_any,
     convert_value_to_struct,
+    set_default_grpc_dns_resolver,
     to_bytes,
     validateNotBlankString,
     validateNotNone,
@@ -189,6 +190,8 @@ def __init__(
             )
             interceptors.append(api_token_interceptor)
 
+        set_default_grpc_dns_resolver()
+
         # Create gRPC channel
         if self._uri.tls:
             self._channel = grpc.aio.secure_channel(

dapr/clients/grpc/_helpers.py

@@ -13,6 +13,9 @@
 limitations under the License.
 """
 
+import logging
+import os
+import sys
 from enum import Enum
 from typing import Any, Dict, List, Optional, Tuple, Union, cast
 
@@ -33,6 +36,27 @@
 MetadataDict = Dict[str, List[Union[bytes, str]]]
 MetadataTuple = Tuple[Tuple[str, Union[bytes, str]], ...]
 
+_logger = logging.getLogger(__name__)
+
+_GRPC_DNS_RESOLVER_ENV = 'GRPC_DNS_RESOLVER'
+_GRPC_DNS_RESOLVER_NATIVE = 'native'
+
+
+def set_default_grpc_dns_resolver() -> None:
+    """Default gRPC to the OS-native DNS resolver on macOS.
+
+    grpcio's bundled c-ares resolver often ignores macOS DNS config and fails
+    with "DNS query cancelled" for endpoints that resolve fine system-wide.
+    Resolver choice is process-wide with no per-channel override, so it is set
+    only on Darwin and only when unset, leaving an explicit value untouched.
+    """
+    if sys.platform != 'darwin':
+        return
+    if _GRPC_DNS_RESOLVER_ENV in os.environ:
+        return
+    os.environ[_GRPC_DNS_RESOLVER_ENV] = _GRPC_DNS_RESOLVER_NATIVE
+    _logger.debug('Defaulted %s=%s on macOS', _GRPC_DNS_RESOLVER_ENV, _GRPC_DNS_RESOLVER_NATIVE)
+
 
 def tuple_to_dict(tupledata: MetadataTuple) -> MetadataDict:
     """Converts tuple to dict.

dapr/clients/grpc/client.py

@@ -44,6 +44,7 @@
     MetadataTuple,
     convert_dict_to_grpc_dict_of_any,
     convert_value_to_struct,
+    set_default_grpc_dns_resolver,
     to_bytes,
     validateNotBlankString,
     validateNotNone,
@@ -169,6 +170,8 @@ def __init__(
         except ValueError as error:
             raise DaprInternalError(f'{error}') from error
 
+        set_default_grpc_dns_resolver()
+
         if self._uri.tls:
             self._channel = grpc.secure_channel(  # type: ignore
                 self._uri.endpoint,

tests/test_grpc_dns_resolver_default.py

@@ -0,0 +1,52 @@
+# -*- coding: utf-8 -*-
+
+"""
+Copyright 2026 The Dapr Authors
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+import unittest
+from unittest import mock
+
+from dapr.clients.grpc import _helpers
+
+_ENV = _helpers._GRPC_DNS_RESOLVER_ENV
+_NATIVE = _helpers._GRPC_DNS_RESOLVER_NATIVE
+
+
+class TestSetDefaultGrpcDnsResolver(unittest.TestCase):
+    def test_sets_native_on_darwin_when_unset(self):
+        with (
+            mock.patch.object(_helpers.sys, 'platform', 'darwin'),
+            mock.patch.dict(_helpers.os.environ, {}, clear=True),
+        ):
+            _helpers.set_default_grpc_dns_resolver()
+            self.assertEqual(_helpers.os.environ[_ENV], _NATIVE)
+
+    def test_preserves_explicit_value_on_darwin(self):
+        with (
+            mock.patch.object(_helpers.sys, 'platform', 'darwin'),
+            mock.patch.dict(_helpers.os.environ, {_ENV: 'ares'}, clear=True),
+        ):
+            _helpers.set_default_grpc_dns_resolver()
+            self.assertEqual(_helpers.os.environ[_ENV], 'ares')
+
+    def test_noop_on_non_darwin(self):
+        with (
+            mock.patch.object(_helpers.sys, 'platform', 'linux'),
+            mock.patch.dict(_helpers.os.environ, {}, clear=True),
+        ):
+            _helpers.set_default_grpc_dns_resolver()
+            self.assertNotIn(_ENV, _helpers.os.environ)
+
+
+if __name__ == '__main__':
+    unittest.main()