Magnum-conductor throws "MultipleResultsFound: Multiple rows were found for one()"

[suibin zhang]

Env: Packstack (Pike) running Magnum. At startup (or restart magnum-conductor service), error in log (Cluster creation failed):

2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task Traceback (most recent call last):
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task File "/usr/lib/python2.7/site-packages/oslo_service/periodic_task.py", line 220, in run_periodic_tasks
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task task(self, context)
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task File "/usr/lib/python2.7/site-packages/magnum/service/periodic.py", line 43, in handler
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task func(self, ctx)
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task File "/usr/lib/python2.7/site-packages/magnum/servicegroup/magnum_service_periodic.py", line 46, in update_magnum_service
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task ctx, self.host, self.binary)
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task File "/usr/lib/python2.7/site-packages/oslo_versionedobjects/base.py", line 184, in wrapper
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task result = fn(cls, context, *args, **kwargs)
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task File "/usr/lib/python2.7/site-packages/magnum/objects/magnum_service.py", line 62, in get_by_host_and_binary
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task host, binary)
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task File "/usr/lib/python2.7/site-packages/magnum/db/sqlalchemy/api.py", line 528, in get_magnum_service_by_host_and_binary
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task return query.one()
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task File "/usr/lib64/python2.7/site-packages/sqlalchemy/orm/query.py", line 2817, in one
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task "Multiple rows were found for one()")
2017-10-14 21:36:05.020 28376 ERROR oslo_service.periodic_task MultipleResultsFound: Multiple rows were found for one()

[suibin zhang (suizh)]

Maybe something went wrong in the initial installation. There are two magnum-conductors running, both in down state. Restarting/re-install did not seem to help.

To solve the problem, drop Magnum + Heat databases, then reinstall packstack with the old answer-file; then the service is running normally.