Failed to launch VM due to no valid host was found

When launch a VM may be failed and see the following error message.

[Error: No valid host was found. Theer are not enough hosts avaiable.]

Default security group created by Neutron for the first time does not exist in the PLUMgrid database, we need to delete it through CLI command.

# neutron net-list
# neutron security-group-list | grep id
# neutron security-group-delete <security-group-id>

new one gets automatically created to PLUMgrid database.

Or we can use Horizon to delete security rules and re-create it.

Failed to lanch VM due to /dev/net/tun

When lauch a VM may be failed and see the following error message

could not open /dev/net/tun: Operation not permitted

Adding /dev/net/tun to the cgroup_device_acl in /etc/libvirt/qemu.conf and then restart libvirtd.

# service libvirtd restart