Python not able to connect to grpc channel -> "failed to connect to all addresses" "grpc_status":14

Question

I'm getting the error below when trying to call a stub method. Any idea what is causing it?

[bolt.api.handlers] 2019-08-21 20:07:57,792 ERROR handlers:1066: 'ResourceHandler' object has no attribute 'ontology_service_handler'
Traceback (most recent call last):
  File "/bolt-webserver/bolt/api/onse/onse_handlers/ontology_service.py", line 17, in post
    ontology_id = await self.onse_stub.createOntology()
  File "/bolt-webserver/bolt/api/onse/onse_stub.py", line 41, in createOntology
    return self.stub.CreateOntology(ontology_messages_pb2.Ontology())
  File "/usr/local/lib/python3.6/site-packages/grpc/_channel.py", line 565, in __call__
    return _end_unary_response_blocking(state, call, False, None)
  File "/usr/local/lib/python3.6/site-packages/grpc/_channel.py", line 467, in _end_unary_response_blocking
    raise _Rendezvous(state, None, None, deadline)
grpc._channel._Rendezvous: <_Rendezvous of RPC that terminated with:
        status = StatusCode.UNAVAILABLE
        details = "failed to connect to all addresses"
        debug_error_string = "{"created":"@1566418077.791002345","description":"Failed to pick subchannel","file":"src/core/ext/filters/client_channel/client_channel.cc","file_line":3818,"referenced_errors":[{"created":"@1566418077.790965749","description":"failed to connect to all addresses","file":"src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc","file_line":395,"grpc_status":14}]}"

I've tried to provide ip address instead of hostname but still getting the same error . The OnseStub class is initialized right before calling createOntology method. The service is up and running. The failing call is done from a tornado web app (in case that might matter)

class OnseStub:

    def __init__(self, ontology_service_backend):
    self.channel = grpc.insecure_channel('localhost:51051')
    self.stub = ontology_service_pb2_grpc.OntologyServiceStub(self.channel)

    def __del__(self):
    if self.channel != None:
    self.channel.close() # close grpc channel

    async def createOntology(self):
    return self.stub.CreateOntology(ontology_messages_pb2.Ontology())

Answer 1

This is common error, it can occured in different cases. But in most usual case decribed in https://github.com/grpc/grpc/issues/9987 can be fixed by unset http_proxy enviroment variable

if os.environ.get('https_proxy'):
 del os.environ['https_proxy']
if os.environ.get('http_proxy'):
 del os.environ['http_proxy']