Comment by Bernd Bausch for Hi. I have a controller and a compute node for test purposes. Yesterday, I successfully was able to create instances. They got IP address, etc, everything was fine. Today, I am not able to create VMs, and the status of the instance is ERROR! root@controller:/# openstack server list +--------------------------------------+---------------------+--------+----------+------------+ | ID | Name | Status | Networks | Image Name | +--------------------------------------+---------------------+--------+----------+------------+ | c59b9cda-3155-4fe8-9b6d-eca702d44431 | provider-instance11 | ERROR | | cirros | +--------------------------------------+---------------------+--------+----------+------------+ This is the log from nova-scheduler on contoller node: 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db dbapi_connection = rec.get_connection() 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db File "/usr/lib/python2.7/dist-packages/sqlalchemy/pool.py", line 563, in get_connection 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db self.connection = self.__connect() 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db File "/usr/lib/python2.7/dist-packages/sqlalchemy/pool.py", line 607, in __connect 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db connection = self.__pool._invoke_creator(self) 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/strategies.py", line 97, in connect 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db return dialect.connect(*cargs, **cparams) 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 385, in connect 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db return self.dbapi.connect(*cargs, **cparams) 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db File "/usr/lib/python2.7/dist-packages/pymysql/__init__.py", line 88, in Connect 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db return Connection(*args, **kwargs) 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db File "/usr/lib/python2.7/dist-packages/pymysql/connections.py", line 679, in __init__ 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db self.connect() 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db File "/usr/lib/python2.7/dist-packages/pymysql/connections.py", line 922, in connect 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db raise exc 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db DBConnectionError: (pymysql.err.OperationalError) (2003, "Can't connect to MySQL server on 'controller' ([Errno 111] ECONNREFUSED)") 2016-12-29 09:50:37.672 4260 ERROR nova.servicegroup.drivers.db 2016-12-29 09:50:46.001 4260 INFO nova.scheduler.host_manager [req-d2c13055-0041-4a6e-baca-351416376d83 - - - - -] Successfully synced instances from host 'compute1'. 2016-12-29 09:50:47.776 4260 INFO nova.servicegroup.drivers.db [-] Recovered from being unable to report status. This is the nova-compute log from the compute node: 2016-12-29 10:33:17.578 3527 INFO nova.compute.resource_tracker [req-22738202-edbf-4306-8744-df2257cea54a - - - - -] Compute_service record updated for compute1:compute1 2016-12-29 10:33:37.780 3527 ERROR nova.service [-] Service error occurred during cleanup_host 2016-12-29 10:33:37.780 3527 ERROR nova.service Traceback (most recent call last): 2016-12-29 10:33:37.780 3527 ERROR nova.service File "/usr/lib/python2.7/dist-packages/nova ... (more)

`Can't connect to MySQL server on 'controller'` could mean the DB connection string in nova.conf is wrong, or MySQL isn't running, or you network or firewall config is incorrect. Or other reasons.