Hi guys.
I'm trying to deploy with "packstack --allinone" and it always (tried ~5 times) fails with:
...
ERROR : Error appeared during Puppet run:A.B.C.D_compute.pp
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: pymysql.err.OperationalError: (1040, 'Too many connections')
You will find full trace in log /var/tmp/packstack/20201018-183415-ik3ijyw7/manifests/172.24.154.202_compute.pp.log
Please check log file /var/tmp/packstack/20201018-183415-ik3ijyw7/openstack-setup.log for more information


If some expert might be interested then in /var/tmp/packstack/20201018-183415-ik3ijyw7/manifests/172.24.154.202_compute.pp.log
....
Notice: /Stage[main]/Nova::Compute::Libvirt/Nova_config[DEFAULT/compute_driver]/ensure: created
Notice: /Stage[main]/Nova::Compute::Libvirt/Nova_config[vnc/server_listen]/ensure: created
Notice: /Stage[main]/Nova::Compute::Libvirt/Nova_config[libvirt/virt_type]/ensure: created
Notice: /Stage[main]/Nova::Compute::Libvirt/Nova_config[libvirt/cpu_mode]/ensure: created
Notice: /Stage[main]/Nova::Compute::Libvirt/Nova_config[libvirt/inject_password]/ensure: created
Notice: /Stage[main]/Nova::Compute::Libvirt/Nova_config[libvirt/inject_key]/ensure: created
Notice: /Stage[main]/Nova::Compute::Libvirt/Nova_config[libvirt/inject_partition]/ensure: created
Notice: /Stage[main]/Nova::Migration::Libvirt/Nova_config[libvirt/live_migration_uri]/ensure: created
Notice: /Stage[main]/Nova::Compute::Libvirt::Services/Service[libvirt]/ensure: ensure changed 'stopped' to 'running'
Notice: /Stage[main]/Neutron::Deps/Anchor[neutron::service::begin]: Triggered 'refresh' from 2 events
Notice: /Stage[main]/Nova::Deps/Anchor[nova::config::end]: Triggered 'refresh' from 22 events
Notice: /Stage[main]/Nova::Deps/Anchor[nova::service::begin]: Triggered 'refresh' from 1 event
Notice: /Stage[main]/Nova::Compute/Nova::Generic_service[compute]/Service[nova-compute]/ensure: ensure changed 'stopped' to 'running'
Notice: /Stage[main]/Nova::Deps/Anchor[nova::service::end]: Triggered 'refresh' from 1 event
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: An error has occurred:
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: Traceback (most recent call last):
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/base.py", line 2262, in _wrap_pool_connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return fn()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 294, in unique_connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return _ConnectionFairy._checkout(self)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 751, in _checkout
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     fairy = _ConnectionRecord.checkout(pool)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 483, in checkout
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     rec = pool._do_get()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/impl.py", line 138, in _do_get
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self._dec_overflow()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     compat.reraise(exc_type, exc_value, exc_tb)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/util/compat.py", line 129, in reraise
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     raise value
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/impl.py", line 135, in _do_get
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return self._create_connection()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 299, in _create_connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return _ConnectionRecord(self)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 428, in __init__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self.__connect(first_connect_check=True)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 630, in __connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     connection = pool._invoke_creator(self)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/strategies.py", line 114, in connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return dialect.connect(*cargs, **cparams)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/default.py", line 453, in connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return self.dbapi.connect(*cargs, **cparams)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/__init__.py", line 94, in Connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return Connection(*args, **kwargs)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 325, in __init__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self.connect()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 599, in connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self._request_authentication()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 861, in _request_authentication
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     auth_packet = self._read_packet()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 684, in _read_packet
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     packet.check_error()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/protocol.py", line 220, in check_error
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     err.raise_mysql_exception(self._data)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/err.py", line 109, in raise_mysql_exception
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     raise errorclass(errno, errval)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: pymysql.err.OperationalError: (1040, 'Too many connections')
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: The above exception was the direct cause of the following exception:
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: Traceback (most recent call last):
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/nova/cmd/manage.py", line 2777, in main
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     ret = fn(*fn_args, **fn_kwargs)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/nova/cmd/manage.py", line 1144, in discover_hosts
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     by_service)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/nova/objects/host_mapping.py", line 256, in discover_hosts
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     cell_mappings = objects.CellMappingList.get_all(ctxt)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_versionedobjects/base.py", line 184, in wrapper
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     result = fn(cls, context, *args, **kwargs)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/nova/objects/cell_mapping.py", line 256, in get_all
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     db_mappings = cls._get_all_from_db(context)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 1013, in wrapper
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     with self._transaction_scope(context):
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/contextlib.py", line 81, in __enter__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return next(self.gen)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 1063, in _transaction_scope
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     context=context) as resource:
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/contextlib.py", line 81, in __enter__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return next(self.gen)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 658, in _session
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     bind=self.connection, mode=self.mode)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 418, in _create_session
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self._start()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 510, in _start
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     engine_args, maker_args)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 534, in _setup_for_connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     sql_connection=sql_connection, **engine_kwargs)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/debtcollector/renames.py", line 43, in decorator
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return wrapped(*args, **kwargs)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/engines.py", line 201, in create_engine
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     test_conn = _test_connection(engine, max_retries, retry_interval)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/oslo_db/sqlalchemy/engines.py", line 376, in _test_connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return engine.connect()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/base.py", line 2193, in connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return self._connection_cls(self, **kwargs)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/base.py", line 103, in __init__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     else engine.raw_connection()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/base.py", line 2293, in raw_connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self.pool.unique_connection, _connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/base.py", line 2266, in _wrap_pool_connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     e, dialect, self
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/base.py", line 1534, in _handle_dbapi_exception_noconnection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     util.raise_from_cause(newraise, exc_info)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/util/compat.py", line 383, in raise_from_cause
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     reraise(type(exception), exception, tb=exc_tb, cause=cause)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/util/compat.py", line 128, in reraise
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     raise value.with_traceback(tb)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/base.py", line 2262, in _wrap_pool_connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return fn()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 294, in unique_connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return _ConnectionFairy._checkout(self)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 751, in _checkout
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     fairy = _ConnectionRecord.checkout(pool)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 483, in checkout
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     rec = pool._do_get()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/impl.py", line 138, in _do_get
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self._dec_overflow()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     compat.reraise(exc_type, exc_value, exc_tb)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/util/compat.py", line 129, in reraise
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     raise value
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/impl.py", line 135, in _do_get
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return self._create_connection()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 299, in _create_connection
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return _ConnectionRecord(self)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 428, in __init__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self.__connect(first_connect_check=True)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/pool/base.py", line 630, in __connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     connection = pool._invoke_creator(self)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/strategies.py", line 114, in connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return dialect.connect(*cargs, **cparams)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib64/python3.6/site-packages/sqlalchemy/engine/default.py", line 453, in connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return self.dbapi.connect(*cargs, **cparams)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/__init__.py", line 94, in Connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     return Connection(*args, **kwargs)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 325, in __init__
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self.connect()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 599, in connect
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     self._request_authentication()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 861, in _request_authentication
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     auth_packet = self._read_packet()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/connections.py", line 684, in _read_packet
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     packet.check_error()
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/protocol.py", line 220, in check_error
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     err.raise_mysql_exception(self._data)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:   File "/usr/lib/python3.6/site-packages/pymysql/err.py", line 109, in raise_mysql_exception
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns:     raise errorclass(errno, errval)
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (1040, 'Too many connections')
Notice: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]/returns: (Background on this error at: http://sqlalche.me/e/e3q8)
Error: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]: Failed to call refresh: 'nova-manage  cell_v2 discover_hosts' returned 255 instead of one of [0]
Error: /Stage[main]/Nova::Cell_v2::Discover_hosts/Exec[nova-cell_v2-discover_hosts]: 'nova-manage  cell_v2 discover_hosts' returned 255 instead of one of [0]

Bit discouraging to fail at start but I trust you can share some good advice.
I'm on Centos8 with ussuri.
Many thanks, L.