轉載地址：http://www.linuxidc.com/Linux/2013-08/88474.htm
最近總玩CloudStack + KVM，發現在重啓CloudStack服務後，host（kvm）的狀態老是爲alert。日誌裏出現如下錯誤提示：
ERROR [agent.manager.AgentManagerImpl] (AgentManager-Handler-7:) Monitor ClusteredVirtualMachineManagerImpl$$EnhancerByCGLIB$$121cf44e says there is an error in the connect process for 1 due to null
java.lang.NullPointerException
at com.cloud.vm.VirtualMachineManagerImpl.fullHostSync(VirtualMachineManagerImpl.java:1643)
at com.cloud.vm.VirtualMachineManagerImpl.processConnect(VirtualMachineManagerImpl.java:2289)
at com.cloud.agent.manager.AgentManagerImpl.notifyMonitorsOfConnection(AgentManagerImpl.java:605)
at com.cloud.agent.manager.AgentManagerImpl.handleConnectedAgent(AgentManagerImpl.java:1157)
at com.cloud.agent.manager.AgentManagerImpl.access$100(AgentManagerImpl.java:142)
at com.cloud.agent.manager.AgentManagerImpl$AgentHandler.processRequest(AgentManagerImpl.java:1235)
at com.cloud.agent.manager.AgentManagerImpl$AgentHandler.doTask(AgentManagerImpl.java:1374)
at com.cloud.agent.manager.ClusteredAgentManagerImpl$ClusteredAgentHandler.doTask(ClusteredAgentManagerImpl.java:618)
at com.cloud.utils.nio.Task.run(Task.java:83)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:679)
agent日誌出現提示：
2013-08-09 11:27:18,746 INFO [cloud.agent.Agent] (Agent-Handler-3:null) Reconnecting...
2013-08-09 11:27:18,747 INFO [utils.nio.NioClient] (Agent-Selector:null) Connecting to 20.1.134.190:8250
2013-08-09 11:27:18,855 INFO [utils.nio.NioClient] (Agent-Selector:null) SSL: Handshake done
2013-08-09 11:27:19,422 INFO [cloud.agent.Agent] (Agent-Handler-2:null) Proccess agent startup answer, agent id = 1
2013-08-09 11:27:19,422 INFO [cloud.agent.Agent] (Agent-Handler-2:null) Set agent id 1
2013-08-09 11:27:19,423 INFO [cloud.agent.Agent] (Agent-Handler-2:null) Startup Response Received: agent id = 1
2013-08-09 11:27:19,539 WARN [cloud.agent.Agent] (UgentTask-5:null) Unable to send request: null
2013-08-09 11:27:23,856 INFO [cloud.agent.Agent] (Agent-Handler-3:null) Connected to the server
2013-08-09 11:27:24,481 INFO [cloud.agent.Agent] (Agent-Handler-3:null) Lost connection to the server. Dealing with the remaining commands...
2013-08-09 11:27:29,483 INFO [cloud.agent.Agent] (Agent-Handler-3:null) Reconnecting...
2013-08-09 11:27:29,484 INFO [utils.nio.NioClient] (Agent-Selector:null) Connecting to 20.1.134.190:8250
2013-08-09 11:27:29,580 INFO [utils.nio.NioClient] (Agent-Selector:null) SSL: Handshake done
2013-08-09 11:27:30,223 INFO [cloud.agent.Agent] (Agent-Handler-2:null) Proccess agent startup answer, agent id = 1
2013-08-09 11:27:30,224 INFO [cloud.agent.Agent] (Agent-Handler-2:null) Set agent id 1
2013-08-09 11:27:30,225 INFO [cloud.agent.Agent] (Agent-Handler-2:null) Startup Response Received: agent id = 1
2013-08-09 11:27:30,350 WARN [cloud.agent.Agent] (UgentTask-5:null) Unable to send request: null
2013-08-09 11:27:34,581 INFO [cloud.agent.Agent] (Agent-Handler-3:null) Connected to the server
2013-08-09 11:27:35,310 INFO [cloud.agent.Agent] (Agent-Handler-3:null) Lost connection to the server. Dealing with the remaining commands...
重啓agent、libvirtd服務，異常依然。重啓host，問題還是一樣。
從日誌中能看出，異常是management-server在連接上cloud-agent後，刷新vm狀態時問題導致的。而此時，除了vRouter，所有vm的狀態均爲Stoped。vRouter的狀態缺爲Running，就此找到問題所在。不知何故，在host上使用virsh list並不能看到vRouter，而management-server卻認爲他是Running狀態，需要刷新一下狀態，導致在management-server查詢不到vRouter，所以拋出異常。這應該是一個bug，需要修復。
解決方案，刪除vRoute（需要先在數據庫將狀態置爲Stopped，執行sql “update vm_instance set state = 'Stopped' where vm_type = 'DomainRouter';”）。
