No sql_connection parameter is established

实验环境为Pike版本，其他版本仅供参考。
在devstack多节点部署中，创建虚机可能会出现下面的错误：

MessageNo sql_connection parameter is establishedCode500DetailsFile "/opt/stack/nova/nova/conductor/manager.py", line 551, in build_instances context, spec_obj, instance_uuids) File "/opt/stack/nova/nova/conductor/manager.py", line 622, in _schedule_instances scheduler_utils.setup_instance_group(context, request_spec) File "/opt/stack/nova/nova/scheduler/utils.py", line 443, in setup_instance_group group_info = _get_group_details(context, instance_uuid, group_hosts) File "/opt/stack/nova/nova/scheduler/utils.py", line 400, in _get_group_details instance_uuid) File "/usr/lib/python2.7/site-packages/oslo_versionedobjects/base.py", line 184, in wrapper result = fn(cls, context, *args, **kwargs) File "/opt/stack/nova/nova/objects/instance_group.py", line 331, in get_by_instance_uuid db_group = cls._get_from_db_by_instance(context, instance_uuid) File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 978, in wrapper with self._transaction_scope(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 1028, 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 633, in _session bind=self.connection, mode=self.mode) File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 398, in _create_session self._start() File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 484, in _start engine_args, maker_args) File "/usr/lib/python2.7/site-packages/oslo_db/sqlalchemy/enginefacade.py", line 506, in _setup_for_connection "No sql_connection parameter is established")CreatedAug. 9, 2017, 6:10 a.m.

原因是缺少数据库连接参数。
在出现问题的节点（一般是计算节点）添加下面的配置项目:

[database]connection = mysql+pymysql://root:secret@192.168.111.69/nova_cell0?charset=utf8[api_database]connection = mysql+pymysql://root:secret@192.168.111.69/nova_api?charset=utf8

这里注意数据库分别是 nova_cell0 为 devstack创建的第一个cell数据库。