Add lb policy example (#32256)

* Add lb policy example

* Update copyright

* This is Python 3

* Fix isort

examples/python/Makefile

@@ -64,6 +64,10 @@ ARTIFACTS += data_transmission/demo_pb2.py
 ARTIFACTS += data_transmission/demo_pb2_grpc.py
 ARTIFACTS += data_transmission/demo_pb2.pyi
 
+ARTIFACTS += lb_policies/helloworld_pb2.py
+ARTIFACTS += lb_policies/helloworld_pb2_grpc.py
+ARTIFACTS += lb_policies/helloworld_pb2.pyi
+
 .PHONY: all
 all: ${ARTIFACTS}
 
@@ -104,6 +108,9 @@ metadata/helloworld_pb2.py metadata/helloworld_pb2_grpc.py metadata/helloworld_p
 data_transmission/demo_pb2.py data_transmission/demo_pb2_grpc.py data_transmission/demo_pb2.pyi: data_transmission/demo.proto
 	python3 -m grpc_tools.protoc --python_out=data_transmission --grpc_python_out=data_transmission --pyi_out=data_transmission -I data_transmission data_transmission/demo.proto
 
+lb_policies/helloworld_pb2.py lb_policies/helloworld_pb2_grpc.py lb_policies/helloworld_pb2.pyi: ../protos/helloworld.proto
+	python3 -m grpc_tools.protoc --python_out=lb_policies --grpc_python_out=lb_policies --pyi_out=lb_policies -I ../protos ../protos/helloworld.proto
+
 .PHONY: clean
 clean:
 	rm -f ${ARTIFACTS}

examples/python/lb_policies/greeter_client.py

@@ -0,0 +1,36 @@
+# Copyright 2023 gRPC 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.
+"""The Python implementation of the GRPC helloworld.Greeter client."""
+
+import logging
+
+import grpc
+import helloworld_pb2
+import helloworld_pb2_grpc
+
+
+def run():
+    print("Will try to greet world ...")
+    options = (("grpc.lb_policy_name", "round_robin"),)
+    # Load balancing takes effect when the DNS server returns multiple IPs for the DNS hostname.
+    # Replace "localhost" with such hostname to see the round robin LB policy take effect.
+    with grpc.insecure_channel('localhost:50051', options=options) as channel:
+        stub = helloworld_pb2_grpc.GreeterStub(channel)
+        response = stub.SayHello(helloworld_pb2.HelloRequest(name='you'))
+    print("Greeter client received: " + response.message)
+
+
+if __name__ == '__main__':
+    logging.basicConfig()
+    run()

examples/python/lb_policies/greeter_server.py

@@ -0,0 +1,42 @@
+# Copyright 2023 gRPC 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.
+"""The Python implementation of the GRPC helloworld.Greeter server."""
+
+from concurrent import futures
+import logging
+
+import grpc
+import helloworld_pb2
+import helloworld_pb2_grpc
+
+
+class Greeter(helloworld_pb2_grpc.GreeterServicer):
+
+    def SayHello(self, request, context):
+        return helloworld_pb2.HelloReply(message='Hello, %s!' % request.name)
+
+
+def serve():
+    port = '50051'
+    server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))
+    helloworld_pb2_grpc.add_GreeterServicer_to_server(Greeter(), server)
+    server.add_insecure_port('[::]:' + port)
+    server.start()
+    print("Server started, listening on " + port)
+    server.wait_for_termination()
+
+
+if __name__ == '__main__':
+    logging.basicConfig()
+    serve()

examples/python/lb_policies/helloworld_pb2.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+# Generated by the protocol buffer compiler.  DO NOT EDIT!
+# source: helloworld.proto
+"""Generated protocol buffer code."""
+from google.protobuf.internal import builder as _builder
+from google.protobuf import descriptor as _descriptor
+from google.protobuf import descriptor_pool as _descriptor_pool
+from google.protobuf import symbol_database as _symbol_database
+# @@protoc_insertion_point(imports)
+
+_sym_db = _symbol_database.Default()
+
+
+
+
+DESCRIPTOR = _descriptor_pool.Default().AddSerializedFile(b'\n\x10helloworld.proto\x12\nhelloworld\"\x1c\n\x0cHelloRequest\x12\x0c\n\x04name\x18\x01 \x01(\t\"\x1d\n\nHelloReply\x12\x0f\n\x07message\x18\x01 \x01(\t2I\n\x07Greeter\x12>\n\x08SayHello\x12\x18.helloworld.HelloRequest\x1a\x16.helloworld.HelloReply\"\x00\x42\x36\n\x1bio.grpc.examples.helloworldB\x0fHelloWorldProtoP\x01\xa2\x02\x03HLWb\x06proto3')
+
+_builder.BuildMessageAndEnumDescriptors(DESCRIPTOR, globals())
+_builder.BuildTopDescriptorsAndMessages(DESCRIPTOR, 'helloworld_pb2', globals())
+if _descriptor._USE_C_DESCRIPTORS == False:
+
+  DESCRIPTOR._options = None
+  DESCRIPTOR._serialized_options = b'\n\033io.grpc.examples.helloworldB\017HelloWorldProtoP\001\242\002\003HLW'
+  _HELLOREQUEST._serialized_start=32
+  _HELLOREQUEST._serialized_end=60
+  _HELLOREPLY._serialized_start=62
+  _HELLOREPLY._serialized_end=91
+  _GREETER._serialized_start=93
+  _GREETER._serialized_end=166
+# @@protoc_insertion_point(module_scope)

examples/python/lb_policies/helloworld_pb2.pyi

@@ -0,0 +1,17 @@
+from google.protobuf import descriptor as _descriptor
+from google.protobuf import message as _message
+from typing import ClassVar as _ClassVar, Optional as _Optional
+
+DESCRIPTOR: _descriptor.FileDescriptor
+
+class HelloReply(_message.Message):
+    __slots__ = ["message"]
+    MESSAGE_FIELD_NUMBER: _ClassVar[int]
+    message: str
+    def __init__(self, message: _Optional[str] = ...) -> None: ...
+
+class HelloRequest(_message.Message):
+    __slots__ = ["name"]
+    NAME_FIELD_NUMBER: _ClassVar[int]
+    name: str
+    def __init__(self, name: _Optional[str] = ...) -> None: ...

examples/python/lb_policies/helloworld_pb2_grpc.py

@@ -0,0 +1,70 @@
+# Generated by the gRPC Python protocol compiler plugin. DO NOT EDIT!
+"""Client and server classes corresponding to protobuf-defined services."""
+import grpc
+
+import helloworld_pb2 as helloworld__pb2
+
+
+class GreeterStub(object):
+    """The greeting service definition.
+    """
+
+    def __init__(self, channel):
+        """Constructor.
+
+        Args:
+            channel: A grpc.Channel.
+        """
+        self.SayHello = channel.unary_unary(
+                '/helloworld.Greeter/SayHello',
+                request_serializer=helloworld__pb2.HelloRequest.SerializeToString,
+                response_deserializer=helloworld__pb2.HelloReply.FromString,
+                )
+
+
+class GreeterServicer(object):
+    """The greeting service definition.
+    """
+
+    def SayHello(self, request, context):
+        """Sends a greeting
+        """
+        context.set_code(grpc.StatusCode.UNIMPLEMENTED)
+        context.set_details('Method not implemented!')
+        raise NotImplementedError('Method not implemented!')
+
+
+def add_GreeterServicer_to_server(servicer, server):
+    rpc_method_handlers = {
+            'SayHello': grpc.unary_unary_rpc_method_handler(
+                    servicer.SayHello,
+                    request_deserializer=helloworld__pb2.HelloRequest.FromString,
+                    response_serializer=helloworld__pb2.HelloReply.SerializeToString,
+            ),
+    }
+    generic_handler = grpc.method_handlers_generic_handler(
+            'helloworld.Greeter', rpc_method_handlers)
+    server.add_generic_rpc_handlers((generic_handler,))
+
+
+ # This class is part of an EXPERIMENTAL API.
+class Greeter(object):
+    """The greeting service definition.
+    """
+
+    @staticmethod
+    def SayHello(request,
+            target,
+            options=(),
+            channel_credentials=None,
+            call_credentials=None,
+            insecure=False,
+            compression=None,
+            wait_for_ready=None,
+            timeout=None,
+            metadata=None):
+        return grpc.experimental.unary_unary(request, target, '/helloworld.Greeter/SayHello',
+            helloworld__pb2.HelloRequest.SerializeToString,
+            helloworld__pb2.HelloReply.FromString,
+            options, channel_credentials,
+            insecure, call_credentials, compression, wait_for_ready, timeout, metadata)