关于instance的powerstate为shutdown的问题

问题描述：服务器（host）关机重启后实例的Powerstate可能会变成shutdown而后实例没法用nova命令或从dashboard启动。

解决方法：

If you use kvm(libvirt), you can logon the compute node. 
use "virsh list --all" list all your no-running vm. For example, there is 
an instance name "instance-00000001", you cannot reboot using nova command 
because it attached block disk. You need do: 
1. virsh undefine instance-0000001 
2. goto the instances dir(default 
/var/lib/nova/instances/instance-00000001), run "virsh define libvirt.xml" 
3. then "virsh start instance-00000001", it can be started now/ 
4. then you should update information about "instances" and "volumes" table 
in nova db. I think you already done it. 
5. then you can "reboot" use nova-client or in dashboard. 

注：上面的方法通常是能够的，不过有时候使用了上面的方法后在dashboard里看到的power state仍是shutdown，这时能够在dashboard里soft reboot一下就能够了

摘自：http://www.gossamer-threads.com/lists/openstack/dev/21524