nova live-migration fails when AZ is not defined and AZs have no shared storage

Issue

Live-migration of instances can fail if Nova has configured NFS for ephemeral storage for instances and when each AZ has a different non-shared NFS share.

The following error message is provided:

[root@server01 ~(keystone_admin)]# nova live-migration e618821e-5875-4300-b5f3-4d5d13508d66
ERROR (BadRequest): instance01.iaas.example.com is not on shared storage: Live migration can not be used without shared storage except a booted from volume VM which does not have a local disk. (HTTP 400) (Request-ID: req-a95d3532-684d-4d91-ac31-82f26f99886a)

And this error trace can be seen in the logs:

2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server [req-a95d3532-684d-4d91-ac31-82f26f99886a 452953354c9248749b8ba119e051c844 8724ebc2beb64ca2a5049069508905fb - - -] Exception during message handling
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server Traceback (most recent call last):
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/server.py", line 133, in _process_incoming
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     res = self.dispatcher.dispatch(message)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 150, in dispatch
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     return self._do_dispatch(endpoint, method, ctxt, args)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 121, in _do_dispatch
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     result = func(ctxt, **new_args)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/nova/exception_wrapper.py", line 75, in wrapped
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     function_name, call_dict, binary)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 220, in __exit__
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     self.force_reraise()
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 196, in force_reraise
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     six.reraise(self.type_, self.value, self.tb)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/nova/exception_wrapper.py", line 66, in wrapped
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     return f(self, context, *args, **kw)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/nova/compute/utils.py", line 613, in decorated_function
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     return function(self, context, *args, **kwargs)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 216, in decorated_function
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     kwargs['instance'], e, sys.exc_info())
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 220, in __exit__
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     self.force_reraise()
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 196, in force_reraise
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     six.reraise(self.type_, self.value, self.tb)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 204, in decorated_function
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     return function(self, context, *args, **kwargs)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 5182, in check_can_live_migrate_source
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     block_device_info)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 5619, in check_can_live_migrate_source
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server     raise exception.InvalidSharedStorage(reason=reason, path=source)
2018-07-10 08:27:09.706 15237 ERROR oslo_messaging.rpc.server InvalidSharedStorage: instance01.iaas.example.com is not on shared storage: Live migration can not be used without shared storage except a booted from volume VM which does not have a local disk.