Exercise 3.2 step 7d - script to join second hypervisor

Hello,
Upon executing script - ./tools/discover_hosts.sh I am facing the following error:
ubuntu@compute-node:~/devstack$ ./tools/discover_hosts.sh
An error has occurred:
Traceback (most recent call last):
File "/opt/stack/nova/nova/cmd/manage.py", line 1923, in main
ret = fn(*fn_args, **fn_kwargs)
File "/opt/stack/nova/nova/cmd/manage.py", line 1631, in discover_hosts
by_service)
File "/opt/stack/nova/nova/objects/host_mapping.py", line 240, in discover_hosts
cell_mappings = objects.CellMappingList.get_all(ctxt)
File "/usr/local/lib/python2.7/dist-packages/oslo_versionedobjects/base.py", line 184, inwrapper
result = fn(cls, context, *args, **kwargs)
File "/opt/stack/nova/nova/objects/cell_mapping.py", line 137, in get_all
db_mappings = cls._get_all_from_db(context)
File "/usr/local/lib/python2.7/dist-packages/oslo_db/sqlalchemy/enginefacade.py", line 980, in wrapper
with self._transaction_scope(context):
File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
File "/usr/local/lib/python2.7/dist-packages/oslo_db/sqlalchemy/enginefacade.py", line 1030, in _transaction_scope
context=context) as resource:
File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
File "/usr/local/lib/python2.7/dist-packages/oslo_db/sqlalchemy/enginefacade.py", line 635, in _session
bind=self.connection, mode=self.mode)
File "/usr/local/lib/python2.7/dist-packages/oslo_db/sqlalchemy/enginefacade.py", line 399, in _create_session
self._start()
File "/usr/local/lib/python2.7/dist-packages/oslo_db/sqlalchemy/enginefacade.py", line 486, in _start
engine_args, maker_args)
File "/usr/local/lib/python2.7/dist-packages/oslo_db/sqlalchemy/enginefacade.py", line 508, in _setup_for_connection
"No sql_connection parameter is established")
CantStartEngineError: No sql_connection parameter is established

ubuntu@compute-node:~/devstack$

Anyone faced the same issue? Can someone help with me this?