This is not an answer, but more information and the code is more readable here then in comments:
2013-12-19 11:43:09.980 ERROR nova.compute.manager [req-68352c27-536d-41ac-95ba-496cf199cf26 7f034b093c9540da9887ec2f147108f3 f70b99e9536a472d881470355164e22b] [instanc
e: 8f36f1c6-288d-459c-b0ca-74e498561a90] Instance failed to spawn
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] Traceback (most recent call last):
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.p
y", line 1119, in _spawn
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] block_device_info)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driv
er.py", line 1531, in spawn
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] block_device_info)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driv
er.py", line 2447, in _create_domain_and_network
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] domain = self._create_domain(xml, instance=instance)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driv
er.py", line 2408, in _create_domain
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] domain.createWithFlags(launch_flags)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", li
ne 187, in doit
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] result = proxy_call(self._autowrap, f, *args, **kwargs)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", li
ne 147, in proxy_call
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] rv = execute(f,*args,**kwargs)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/eventlet/tpool.py", li
ne 76, in tworker
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] rv = meth(*args,**kwargs)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/libvirt.py", line 711,
in createWithFlags
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] if ret == -1: raise libvirtError ('virDomainCreateWithFlags
() failed', dom=self)
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] libvirtError: Unable to read from monitor: Connection reset by
peer
2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90]
2013-12-19 11:43:12.030 ERROR nova.compute.manager [req-68352c27-536d-41ac-95ba-496cf199cf26 7f034b093c9540da9887ec2f147108f3 f70b99e9536a472d881470355164e22b] [instanc
e: 8f36f1c6-288d-459c-b0ca-74e498561a90] Error: ['Traceback (most recent call last):\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 864, i
n _run_instance\n set_access_ip=set_access_ip)\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1123, in _spawn\n LOG.exception(_(\'In
stance failed to spawn\'), instance=instance)\n ...
(more)
I'm not clear: are you saying that /var/lib/nova/instances/420926e7-f1f8-4d82-ad93-29de9aca7f77/disk actually exists on the filesystem? If so, it it (and everything under /var/lib/nova) owned by the "nova" user?
That file did exist, I am sure after researching other places that one may have been a UUID conflict. So, I tried again and get a more fruitful result...still fails, but more informative errors (to Python folks anyway).. 2013-12-19 11:43:09.980 ERROR nova.compute.manager [req-68352c27-536d-41ac-95ba-496cf199cf26 7f034b093c9540da9887ec2f147108f3 f70b99e9536a472d881470355164e22b] [instanc e: 8f36f1c6-288d-459c-b0ca-74e498561a90] Instance failed to spawn 2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] Traceback (most recent call last): 2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.p y", line 1119, in _spawn 2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288d-459c-b0ca-74e498561a90] block_device_info) 2013-12-19 11:43:09.980 1525 TRACE nova.compute.manager [instance: 8f36f1c6-288
Is `libvirtd` running on your compute node (can you run "virsh list" on the compute node without errors)? Are you certain that your compute node has sufficient memory for what you're trying to do? Lack of memory can often manifest in strange ways with unhelpful error messages.