CloudStack Host 状态机 (4)

书接上文：[CloudStack Host 状态机 (3)]

状态机初始状态为null或Creating，没有任何Event可以把状态修改回初始状态。
最终状态为Removed，此时该状态不接受任何Event。
异常状态为Alert，Error。
中间状态为Up,Down ,Connecting, Disconnected, Rebalancing。
null只能接受AgentConnected，Error只能接受AgentConnected。

s_fsm.addTransition(null, Event.AgentConnected, Status.Connecting);
s_fsm.addTransition(Status.Creating, Event.AgentConnected, Status.Connecting);

创建过程：如果初始状态为null或Creating，接到Event为AgentConnected，状态变为Connecting，初始状态为null只能接受AgentConnected

s_fsm.addTransition(Status.Creating, Event.Error, Status.Error);

创建过程：如果初始状态为Creating，接到Event为Error，状态变为Error

s_fsm.addTransition(Status.Connecting, Event.AgentConnected, Status.Connecting);
s_fsm.addTransition(Status.Connecting, Event.Ready, Status.Up);
s_fsm.addTransition(Status.Connecting, Event.PingTimeout, Status.Alert);
s_fsm.addTransition(Status.Connecting, Event.ShutdownRequested, Status.Disconnected);
s_fsm.addTransition(Status.Connecting, Event.HostDown, Status.Alert);
s_fsm.addTransition(Status.Connecting, Event.Ping, Status.Connecting);
s_fsm.addTransition(Status.Connecting, Event.ManagementServerDown, Status.Disconnected);
s_fsm.addTransition(Status.Connecting, Event.AgentDisconnected, Status.Alert);

连接过程：根据接到的Event来判断是否成功并把状态置为相应状态。Connecting不会转变为Error，Rebalancing，Removed。

s_fsm.addTransition(Status.Up, Event.PingTimeout, Status.Alert);
s_fsm.addTransition(Status.Up, Event.AgentDisconnected, Status.Alert);
s_fsm.addTransition(Status.Up, Event.ShutdownRequested, Status.Disconnected);
s_fsm.addTransition(Status.Up, Event.HostDown, Status.Down);
s_fsm.addTransition(Status.Up, Event.Ping, Status.Up);
s_fsm.addTransition(Status.Up, Event.AgentConnected, Status.Connecting);
s_fsm.addTransition(Status.Up, Event.ManagementServerDown, Status.Disconnected);
s_fsm.addTransition(Status.Up, Event.StartAgentRebalance, Status.Rebalancing);
s_fsm.addTransition(Status.Up, Event.Remove, Status.Removed);

Up为正常连接状态，会随着接受到各种事件，转变为其它中间状态。

s_fsm.addTransition(Status.Disconnected, Event.PingTimeout, Status.Alert);
s_fsm.addTransition(Status.Disconnected, Event.AgentConnected, Status.Connecting);
s_fsm.addTransition(Status.Disconnected, Event.Ping, Status.Up);
s_fsm.addTransition(Status.Disconnected, Event.HostDown, Status.Down);
s_fsm.addTransition(Status.Disconnected, Event.ManagementServerDown, Status.Disconnected);
s_fsm.addTransition(Status.Disconnected, Event.WaitedTooLong, Status.Alert);
s_fsm.addTransition(Status.Disconnected, Event.Remove, Status.Removed);
s_fsm.addTransition(Status.Disconnected, Event.AgentDisconnected, Status.Disconnected);

Disconnected为连接断开，Ping失败，监控线程发现断开，都可能变为该状态，该状态接受各种Event也会变为相应下一步状态。

s_fsm.addTransition(Status.Down, Event.AgentConnected, Status.Connecting);
s_fsm.addTransition(Status.Down, Event.Remove, Status.Removed);
s_fsm.addTransition(Status.Down, Event.ManagementServerDown, Status.Down);
s_fsm.addTransition(Status.Down, Event.AgentDisconnected, Status.Down);
s_fsm.addTransition(Status.Down, Event.PingTimeout, Status.Down);

Down为主机或Host关机状态，Agent连接成功，会变为Connecting进入下一步状态机。

s_fsm.addTransition(Status.Alert, Event.AgentConnected, Status.Connecting);
s_fsm.addTransition(Status.Alert, Event.Ping, Status.Up);
s_fsm.addTransition(Status.Alert, Event.Remove, Status.Removed);
s_fsm.addTransition(Status.Alert, Event.ManagementServerDown, Status.Alert);
s_fsm.addTransition(Status.Alert, Event.AgentDisconnected, Status.Alert);
s_fsm.addTransition(Status.Alert, Event.ShutdownRequested, Status.Disconnected);

Alert主机状态发生异常而进行重启（丢失主存储）或断网，都可能导致Alert状态，随后Agent连接则重新变为Connecting等状态。

s_fsm.addTransition(Status.Rebalancing, Event.RebalanceFailed, Status.Disconnected);
s_fsm.addTransition(Status.Rebalancing, Event.RebalanceCompleted, Status.Connecting);
s_fsm.addTransition(Status.Rebalancing, Event.ManagementServerDown, Status.Disconnected);
s_fsm.addTransition(Status.Rebalancing, Event.AgentConnected, Status.Connecting);
s_fsm.addTransition(Status.Rebalancing, Event.AgentDisconnected, Status.Rebalancing);

Rebalancing接受Rebalance调度任务之后的中间状态

s_fsm.addTransition(Status.Error, Event.AgentConnected, Status.Connecting);

任何状态改变流程出现InternalError都可能引发状态变为Error。