Kubernetes 的PodPhase归纳

参考官网文档：http://kubernetes.io/docs/user-guide/pod-states/

介绍pod生命周期的blog ：http://blog.youkuaiyun.com/horsefoot/article/details/52324830（比较详细 ）

一下图片摘自以上blog：

Pod的状态 

• Pending: The pod has been accepted by the system, but one or more of the container images has not been created. This includes time before being scheduled as well as time spent downloading images over the network, which could take a while.

   系统已经接收了创建了pod的请求，但是其中有部分容器未创建。这包括容器调度、镜像下载等需要花费一段时间。

• Running: The pod has been bound to a node, and all of the containers have been created. At least one container is still running, or is in the process of starting or restarting.

   pod已经被绑定在某个node上了，所有的容器都已经被创建，至少有一个容器任然在运行、启动、重启状态。

• Succeeded: All containers in the pod have terminated in success, and will not be restarted.

   pod上的所有容器都已经被成功停止，并且不会再被重启。

• Failed: All containers in the pod have terminated, at least one container has terminated in failure (exited with non-zero exit status or was terminated by the system).

   所有容器都终止运行，至少有一个容器停止失败（非正常状态推出或者被系统终止运行）

• Unknown: For some reason the state of the pod could not be obtained, typically due to an error in communicating with the host of the pod

    由于某些原因，pod的运行阶段无法获取，通常是因为与pod所在主机发生通信故障（无法连接）。

Pod LifeTime

pod的状态不完全取决于容器的状态，还与RestartPolicy 重启策略有关 。

Termination of Pods

简单来说，就是会有一个延迟来处理pod的资源释放等。用户可以自定义强制killpod的前的一段时间做clear up。

Because pods represent running processes on nodes in the cluster, 
it is important to allow those processes to gracefully terminate 
when they are no longer needed (vs being violently killed with a
 KILL signal and having no chance to clean up). Users should be 
 able to request deletion and know when processes terminate,
 but also be able to ensure that deletes eventually complete.
 When a user requests deletion of a pod the system records the intended grace period
 before the pod is allowed to be forcefully killed, 
 and a TERM signal is sent to the main process in each container. 
 Once the grace period has expired the KILL signal is sent to those processes 
 and the pod is then deleted from the API server. If the Kubelet or the container manager 
 is restarted while waiting for processes to terminate, the termination will be retried 
 with the full grace period. 

Pod中的容器状态：

Waiting

Running

Terminated