Python InactiveRpcError failed to connect to all addresses

[raphael ambrosius]

Hi I am trying to write a test grpc client and service in python. When I use an insecure channel, everything works stably, but if I try to establish a tls connection, an error occurs. To write code and create a chain of certificates, I used this guide.How can I make this example work?
grpcio version : 1.51.1 python version 3.9.17

Error message:

Message = <_InactiveRpcError of RPC that terminated with:
    status = StatusCode.UNAVAILABLE
    details = "failed to connect to all addresses"
    debug_error_string = "{"created":"@1690999363.720000000","description":"Failed to pick subchannel","file":"src/core/ext/filters/client_channel/client_channel.cc","file_line":3094,"referenced_errors":[{"created":"@1690999363.720000000","description":"failed to connect to all addresses","file":"src/core/lib/transport/error_utils.cc","file_line":163,"grpc_status":14}]}"
>
  Source = F:\Work\PytService\ClientPy\ClientPy.py
  Stack trace:
  File "F:\Work\PytService\ClientPy\ClientPy.py", line 22, in run
    response = stub.SayHello(service_pb2.HelloRequest(name='you'))
  File "F:\Work\PytService\ClientPy\ClientPy.py", line 32, in <module> (Current frame)
    run()
grpc._channel._InactiveRpcError: <_InactiveRpcError of RPC that terminated with:
    status = StatusCode.UNAVAILABLE
    details = "failed to connect to all addresses"
    debug_error_string = "{"created":"@1690999363.720000000","description":"Failed to pick subchannel","file":"src/core/ext/filters/client_channel/client_channel.cc","file_line":3094,"referenced_errors":[{"created":"@1690999363.720000000","description":"failed to connect to all addresses","file":"src/core/lib/transport/error_utils.cc","file_line":163,"grpc_status":14}]}"
>

Service code

from concurrent import futures
import logging
import grpc
import service_pb2
import service_pb2_grpc


class Greeter(service_pb2_grpc.GreeterServicer):

    def SayHello(self, request, context):
        return service_pb2.HelloReply(message='Hello, %s!' % request.name)
    def SayHelloAgain(self, request, context):
        return service_pb2.HelloReply(message=f'Hello again, {request.name}!')

def serve():
    port = '50051'
    server_host = 'localhost'
    server = grpc.server(futures.ThreadPoolExecutor(max_workers=10))
    service_pb2_grpc.add_GreeterServicer_to_server(Greeter(), server)

    keyfile = 'server-key.pem'
    certfile = 'server-cert.pem'
    private_key = open(keyfile).read()
    certificate_chain = open(certfile).read()
    credentials = grpc.ssl_server_credentials(
       ((bytes(private_key, 'utf-8'), bytes(certificate_chain, 'utf-8'),),)
    )
    server.add_secure_port('localhost:50001',credentials)
    server.start()
    print("Server started, listening on " + port)
    server.wait_for_termination()


if __name__ == '__main__':
    logging.basicConfig()
    serve()

Client code

from __future__ import print_function
import logging
import grpc
import grpc_tools
import service_pb2
import service_pb2_grpc


def run():
      ca_cert = 'ca-cert.pem'
      root_certs = open(ca_cert).read()
      credentials = grpc.ssl_channel_credentials((bytes(root_certs, 'utf-8')))
      with grpc.secure_channel('localhost:50051',credentials) as channel:
          stub = service_pb2_grpc.GreeterStub(channel)
          response = stub.SayHello(service_pb2.HelloRequest(name='you'))
          print("Greeter client received: " + response.message)
          response = stub.SayHelloAgain(service_pb2.HelloRequest(name='you1'))
          print("Greeter client received: " + response.message)


if __name__ == '__main__':
    logging.basicConfig()
    run()

I tried to change certificates, creating them not only according to the manual, but also using openssl. And also change the encryption method for certificates from RSA to P-256 curve. But none of the above helped.