Cannot launch instance from Horizon

Issue

• I cannot launch an instance in the OpenStack GUI, it gives an error message below when using a m1.large flavor:

2016-04-12 11:40:46.545 940 WARNING nova.scheduler.utils [req-<id> - - -] Failed to compute_task_build_instances: No valid host was found. There are not enough hosts available.
Traceback (most recent call last):

  File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/server.py", line 142, in inner
    return func(*args, **kwargs)

  File "/usr/lib/python2.7/site-packages/nova/scheduler/manager.py", line 86, in select_destinations
    filter_properties)

  File "/usr/lib/python2.7/site-packages/nova/scheduler/filter_scheduler.py", line 80, in select_destinations
    raise exception.NoValidHost(reason=reason)

NoValidHost: No valid host was found. There are not enough hosts available.

• After enabling debug logging, this is seen when attempting to launch the instance:

2016-05-04 11:18:51.535 2224 ERROR nova.compute.manager [req-<id> - - -] [instance: <uuid>] Instance failed to spawn
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>] Traceback (most recent call last):
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2486, in _build_resources
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     yield resources
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2358, in _build_and_run_instance
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     block_device_info=block_device_info)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 2580, in spawn
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     block_device_info=block_device_info)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 4659, in _create_domain_and_network
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     power_on=power_on)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 4590, in _create_domain
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     LOG.error(err)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 85, in __exit__
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     six.reraise(self.type_, self.value, self.tb)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 4580, in _create_domain
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     domain.createWithFlags(launch_flags)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 183, in doit
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     result = proxy_call(self._autowrap, f, *args, **kwargs)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 141, in proxy_call
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     rv = execute(f, *args, **kwargs)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 122, in execute
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     six.reraise(c, e, tb)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/eventlet/tpool.py", line 80, in tworker
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     rv = meth(*args, **kwargs)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib64/python2.7/site-packages/libvirt.py", line 1059, in createWithFlags
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]     if ret == -1: raise libvirtError ('virDomainCreateWithFlags() failed', dom=self)
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>] libvirtError: internal error: process exited while connecting to monitor: 2016-05-04T15:18:51.381857Z qemu-kvm: cannot set up guest memory 'pc.ram': Cannot allocate memory
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]
2016-05-04 11:18:51.535 2224 TRACE nova.compute.manager [instance: <uuid>]
2016-05-04 11:18:51.545 2224 INFO nova.compute.manager [req-<id> - - -] [instance: <uuid>] Terminating instance
2016-05-04 11:18:51.549 2224 INFO nova.virt.libvirt.driver [-] [instance: <uuid>] Instance destroyed successfully.
2016-05-04 11:18:51.549 2224 DEBUG oslo_concurrency.processutils [req-<id> - - -] Running cmd (subprocess): mv /var/lib/nova/instances/<uuid> /var/lib/nova/instances/<uuid>_del execute /usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py:223
2016-05-04 11:18:51.557 2224 DEBUG oslo_concurrency.processutils [req-<id> - - -] CMD "mv /var/lib/nova/instances/<uuid> /var/lib/nova/instances/<uuid>_del" returned: 0 in 0.008s execute /usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py:254
2016-05-04 11:18:51.558 2224 INFO nova.virt.libvirt.driver [req-<id> - - -] [instance: <uuid>] Deleting instance files /var/lib/nova/instances/<uuid>_del
2016-05-04 11:18:51.558 2224 INFO nova.virt.libvirt.driver [req-<id> - - -] [instance: <uuid>] Deletion of /var/lib/nova/instances/<uuid>_del complete
2016-05-04 11:18:51.653 2224 DEBUG nova.compute.claims [req-<id> - - -] [instance: <uuid>] Aborting claim: [Claim: 4096 MB memory, 40 GB disk] abort /usr/lib/python2.7/site-packages/nova/compute/claims.py:130