Something very similar to this came up in another run, but at a slightly different place:

2019-04-23 12:39:50 ERROR juju-log identity-credentials:240: Hook error:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 601, in urlopen
    chunked=chunked)
  File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 387, in _make_request
    six.raise_from(e, None)
  File "<string>", line 3, in raise_from
  File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 383, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/lib/python3.6/http/client.py", line 1331, in getresponse
    response.begin()
  File "/usr/lib/python3.6/http/client.py", line 297, in begin
    version, status, reason = self._read_status()
  File "/usr/lib/python3.6/http/client.py", line 266, in _read_status
    raise RemoteDisconnected("Remote end closed connection without"
http.client.RemoteDisconnected: Remote end closed connection without response

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/requests/adapters.py", line 440, in send
    timeout=timeout
  File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 639, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "/usr/lib/python3/dist-packages/urllib3/util/retry.py", line 357, in increment
    raise six.reraise(type(error), error, _stacktrace)
  File "/var/lib/juju/agents/unit-openstack-service-checks-0/.venv/lib/python3.6/site-packages/six.py", line 692, in reraise
    raise value.with_traceback(tb)
  File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 601, in urlopen
    chunked=chunked)
  File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 387, in _make_request
    six.raise_from(e, None)
  File "<string>", line 3, in raise_from
  File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 383, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/lib/python3.6/http/client.py", line 1331, in getresponse
    response.begin()
  File "/usr/lib/python3.6/http/client.py", line 297, in begin
    version, status, reason = self._read_status()
  File "/usr/lib/python3.6/http/client.py", line 266, in _read_status
    raise RemoteDisconnected("Remote end closed connection without"
urllib3.exceptions.ProtocolError: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response',))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/keystoneclient/session.py", line 462, in _send_request
    resp = self.session.request(method, url, **kwargs)
  File "/usr/lib/python3/dist-packages/requests/sessions.py", line 520, in request
    resp = self.send(prep, **send_kwargs)
  File "/usr/lib/python3/dist-packages/requests/sessions.py", line 630, in send
    r = adapter.send(request, **kwargs)
  File "/usr/lib/python3/dist-packages/requests/adapters.py", line 490, in send
    raise ConnectionError(err, request=request)
requests.exceptions.ConnectionError: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response',))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-openstack-service-checks-0/.venv/lib/python3.6/site-packages/charms/reactive/__init__.py", line 73, in main
    bus.dispatch(restricted=restricted_mode)
  File "/var/lib/juju/agents/unit-openstack-service-checks-0/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 390, in dispatch
    _invoke(other_handlers)
  File "/var/lib/juju/agents/unit-openstack-service-checks-0/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 359, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-openstack-service-checks-0/.venv/lib/python3.6/site-packages/charms/reactive/bus.py", line 181, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-openstack-service-checks-0/charm/reactive/openstack_service_checks.py", line 165, in render_config
    helper.render_checks(creds)
  File "lib/lib_openstack_service_checks.py", line 140, in render_checks
    self.create_endpoint_checks(creds)
  File "lib/lib_openstack_service_checks.py", line 178, in create_endpoint_checks
    endpoints = keystone_client.endpoints.list()
  File "/usr/lib/python3/dist-packages/keystoneclient/v3/endpoints.py", line 125, in list
    **kwargs)
  File "/usr/lib/python3/dist-packages/keystoneclient/base.py", line 75, in func
    return f(*args, **new_kwargs)
  File "/usr/lib/python3/dist-packages/keystoneclient/base.py", line 397, in list
    self.collection_key)
  File "/usr/lib/python3/dist-packages/keystoneclient/base.py", line 125, in _list
    resp, body = self.client.get(url, **kwargs)
  File "/usr/lib/python3/dist-packages/keystoneauth1/adapter.py", line 304, in get
    return self.request(url, 'GET', **kwargs)
  File "/usr/lib/python3/dist-packages/keystoneauth1/adapter.py", line 463, in request
    resp = super(LegacyJsonAdapter, self).request(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/keystoneauth1/adapter.py", line 189, in request
    return self.session.request(url, method, **kwargs)
  File "/usr/lib/python3/dist-packages/keystoneclient/session.py", line 343, in request
    auth_headers = self.get_auth_headers(auth)
  File "/usr/lib/python3/dist-packages/keystoneclient/session.py", line 660, in get_auth_headers
    return auth.get_headers(self, **kwargs)
  File "/usr/lib/python3/dist-packages/keystoneclient/auth/base.py", line 159, in get_headers
    token = self.get_token(session)
  File "/usr/lib/python3/dist-packages/keystoneclient/auth/identity/base.py", line 206, in get_token
    return self.get_access(session).auth_token
  File "/usr/lib/python3/dist-packages/keystoneclient/auth/identity/base.py", line 252, in get_access
    self.auth_ref = self.get_auth_ref(session)
  File "/usr/lib/python3/dist-packages/keystoneclient/auth/identity/v3/base.py", line 189, in get_auth_ref
    authenticated=False, log=False, **rkwargs)
  File "/usr/lib/python3/dist-packages/keystoneclient/session.py", line 543, in post
    return self.request(url, 'POST', **kwargs)
  File "/usr/lib/python3/dist-packages/keystoneclient/session.py", line 428, in request
    resp = send(**kwargs)
  File "/usr/lib/python3/dist-packages/keystoneclient/session.py", line 472, in _send_request
    raise exceptions.ConnectionRefused(msg)
keystoneauth1.exceptions.connection.ConnectFailure: Unable to establish connection to http://10.244.40.88:35357/v3/auth/tokens

2019-04-23 12:39:50 ERROR juju.worker.uniter.operation runhook.go:132 hook "identity-credentials-relation-changed" failed: exit status 1
2019-04-23 12:39:50 INFO juju.worker.uniter resolver.go:124 awaiting error resolution for "relation-changed" hook
2019-04-23 12:39:55 INFO juju.worker.uniter resolver.go:124 awaiting error resolution for "relation-changed" hook
2019-04-23 12:39:55 INFO juju-log identity-credentials:240: Reactive main running for hook identity-credentials-relation-changed