bash-4.2$ /usr/bin/nova-manage cell_v2 discover_hosts --by-service --verbose
Found 2 cell mappings.
Skipping cell0 since it does not contain hosts.
Getting computes from cell 'default': 7e326f37-322a-4cdc-94a2-d4c3db58ac4a
An error has occurred:
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/nova/cmd/manage.py", line 2212, in main
    ret = fn(*fn_args, **fn_kwargs)
  File "/usr/lib/python2.7/site-packages/nova/cmd/manage.py", line 1303, in discover_hosts
    by_service)
  File "/usr/lib/python2.7/site-packages/nova/objects/host_mapping.py", line 265, in discover_hosts
    by_service)
  File "/usr/lib/python2.7/site-packages/nova/objects/host_mapping.py", line 221, in _check_and_create_host_mappings
    ctxt, 'nova-compute', include_disabled=True)
  File "/usr/lib/python2.7/site-packages/oslo_versionedobjects/base.py", line 184, in wrapper
    result = fn(cls, context, *args, **kwargs)
  File "/usr/lib/python2.7/site-packages/nova/objects/service.py", line 591, in get_by_binary
    context, binary, include_disabled=include_disabled)
  File "/usr/lib/python2.7/site-packages/nova/db/api.py", line 145, in service_get_all_by_binary
    include_disabled=include_disabled)
  File "/usr/lib/python2.7/site-packages/nova/db/sqlalchemy/api.py", line 228, in wrapped
    with ctxt_mgr.reader.using(context):
  File "/usr/lib64/python2.7/contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 1064, in _transaction_scope
    context=context) as resource:
  File "/usr/lib64/python2.7/contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 659, in _session
    bind=self.connection, mode=self.mode)
  File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 418, in _create_session
    self._start()
  File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 510, in _start
    engine_args, maker_args)
  File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 534, in _setup_for_connection
    sql_connection=sql_connection, **engine_kwargs)
  File "/usr/lib/python2.7/site-packages/debtcollector/renames.py", line 43, in decorator
    return wrapped(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/engines.py", line 153, in create_engine
    url = sqlalchemy.engine.url.make_url(sql_connection)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/url.py", line 225, in make_url
    return _parse_rfc1738_args(name_or_url)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/url.py", line 284, in _parse_rfc1738_args
    return URL(name, **components)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/url.py", line 71, in __init__
    self.port = int(port)
ValueError: invalid literal for int() with base 10: '3456:789a:1::3'

######################################################################
###### Apply patch: https://review.opendev.org/664559 manually. #####
bash-4.2$ vi lib/python2.7/site-packages/nova/objects/cell_mapping.py                                                                                                                                                                               
######################################################################

bash-4.2$ /usr/bin/nova-manage cell_v2 discover_hosts --by-service --verbose                                                                                                                                                                        
Found 2 cell mappings.
Skipping cell0 since it does not contain hosts.
Getting computes from cell 'default': 7e326f37-322a-4cdc-94a2-d4c3db58ac4a
Creating host mapping for service undercloud.localdomain
Found 1 unmapped computes in cell: 7e326f37-322a-4cdc-94a2-d4c3db58ac4a