##k8s pod 状态分析
pod从创建到最后的创建成功会分别处于不同的阶段，在源码中用PodPhase来表示不同的阶段：
PodPending PodPhase = "Pending" PodRunning PodPhase = "Running" PodSucceeded PodPhase = "Succeeded" PodFailed PodPhase = "Failed" PodUnknown PodPhase = "Unknown"一个pod的完整创建，通常会伴随着各种事件的产生，k8s种事件的种类总共只有4种：
Added EventType = "ADDED" Modified EventType = "MODIFIED" Deleted EventType = "DELETED" Error EventType = "ERROR" Pending 创建pod的请求已经被k8s接受，但是容器并没有启动成功，可能处在：写数据到etcd，调度，pull镜像，启动容器这四个阶段中的任何一个阶段，pending伴随的事件通常会有：ADDED, Modified这两个事件的产生。Running pod已经绑定到node节点，并且所有的容器已经启动成功，或者至少有一个容器在运行，或者在重启中。Succeeded pod中的所有的容器已经正常的自行退出，并且k8s永远不会自动重启这些容器，一般会是在部署job的时候会出现。Failed pod中的所有容器已经终止，并且至少有一个容器已经终止于失败（退出非零退出代码或被系统停止）。Unknown 由于某种原因，无法获得pod的状态，通常是由于与pod的主机通信错误。以上说到的pod的状态是粗略的状态，还有更佳详细的状态信息，在源码中表示如下：
PodScheduled PodConditionType = "PodScheduled" PodReady PodConditionType = "Ready" PodInitialized PodConditionType = "Initialized" PodReasonUnschedulable = "Unschedulable" type PodCondition struct { Type PodConditionType `json:"type" protobuf:"bytes,1,opt,name=type,casttype=PodConditionType"` Status ConditionStatus `json:"status" protobuf:"bytes,2,opt,name=status,casttype=ConditionStatus"` LastProbeTime metav1.Time `json:"lastProbeTime,omitempty" protobuf:"bytes,3,opt,name=lastProbeTime"` LastTransitionTime metav1.Time `json:"lastTransitionTime,omitempty" protobuf:"bytes,4,opt,name=lastTransitionTime"` Reason string `json:"reason,omitempty" protobuf:"bytes,5,opt,name=reason"` Message string `json:"message,omitempty" protobuf:"bytes,6,opt,name=message"` } PodScheduled pod正处于调度中，刚开始调度的时候，hostip还没绑定上，持续调度之后，有合适的节点就会绑定hostip，然后更新etcd数据Initialized pod中的所有初始化容器已经初启动完毕Ready pod中的容器可以提供服务了Unschedulable 不能调度，没有合适的节点PodCondition中的ConditionStatus，它代表了当前pod是否处于某一个阶段（PodScheduled，Ready，Initialized，Unschedulable），“true” 表示处于，“false”表示不处于
以下通过创建一个pod来具体的看看从pod创建到成功所触发的事件，以及pod相关状态的改变
kubectl apply -f busybox.yaml第一步：写入数据到etcd
event type: ADDED event object: { "phase": "Pending", "qosClass": "BestEffort" }第二步：开始被调度，但是还未调度到具体node上，请注意：PodScheduled的status=“true”
event type: MODIFIED { "phase": "Pending", "conditions": [ { "type": "PodScheduled", "status": "True", "lastProbeTime": null, "lastTransitionTime": "2017-06-06T07:57:06Z" } ], "qosClass": "BestEffort" }第三步：被调度到了具体的node上hostip绑定了，并且被所有初始化容器已经启动完毕（注意我的busybox.yaml中pod没有指定init container，所以这里很快就被设置成true）,被调度到的节点watch到并开始创建容器（此阶段是在拉去镜像）然后创建容器 ，而此时Ready的status是false，仔细看会发现，containerStatus的状态未waiting
event type: MODIFIED { "phase": "Pending", "conditions": [ { "type": "Initialized", "status": "True", "lastProbeTime": null, "lastTransitionTime": "2017-06-06T07:57:06Z" }, { "type": "Ready", "status": "False", "lastProbeTime": null, "lastTransitionTime": "2017-06-06T07:57:06Z", "reason": "ContainersNotReady", "message": "containers with unready status: [busybox]" }, { "type": "PodScheduled", "status": "True", "lastProbeTime": null, "lastTransitionTime": "2017-06-06T07:57:06Z" } ], "hostIP": "10.39.1.35", "startTime": "2017-06-06T07:57:06Z", "containerStatuses": [ { "name": "busybox", "state": { "waiting": { "reason": "ContainerCreating" } }, "lastState": {}, "ready": false, "restartCount": 0, "image": "busybox", "imageID": "" } ], "qosClass": "BestEffort" }第四步：容器创建成功，Ready的status=“true”，此时容器的status也为running，这个时候，对应的pod的PodPhase也应该为running
event type: MODIFIED { "phase": "Running", "conditions": [ { "type": "Initialized", "status": "True", "lastProbeTime": null, "lastTransitionTime": "2017-06-06T07:57:06Z" }, { "type": "Ready", "status": "True", "lastProbeTime": null, "lastTransitionTime": "2017-06-06T07:57:08Z" }, { "type": "PodScheduled", "status": "True", "lastProbeTime": null, "lastTransitionTime": "2017-06-06T07:57:06Z" } ], "hostIP": "10.39.1.35", "podIP": "192.168.107.204", "startTime": "2017-06-06T07:57:06Z", "containerStatuses": [ { "name": "busybox", "state": { "running": { "startedAt": "2017-06-06T07:57:08Z" } }, "lastState": {}, "ready": true, "restartCount": 0, "image": "busybox:latest", "imageID": "docker-pullable://busybox@sha256:c79345819a6882c31b41bc771d9a94fc52872fa651b36771fbe0c8461d7ee558", "containerID": "docker://a6af9d58c7dabf55fdfe8d4222b2c16349e3b49b3d0eca4bc761fdb571f3cf44" } ], "qosClass": "BestEffort" }