Kubernetes pod状态出现ImagePullBackOff的原因

通过一个试验作为例子来学习一下。

我们创建一个名为fail 的 deployment，让它故意指向一个实际并不存在的 Docker 镜像：
$ kubectl run fail --image=jerry/sap:v1.0.0

查看这个Pod的状态，发现状态为 ErrImagePull 或者 ImagePullBackOff：

$ kubectl get pods
NAME READY STATUS RESTARTS AGE
fail-1034443984-jerry 0/1 ImagePullBackOff 0 2m

可以使用describe命令查看这个失败的Pod的明细：
$ kubectl describe pod fail-1034443984-jerry

查看 describe 命令的输出中 Events 这部分，我们可以看到如下内容：

Events:
FirstSeen LastSeen Count From SubObjectPath Type Reason Message

5m 5m 1 {default-scheduler } Normal Scheduled Successfully assigned fail-1034443984-jerry to gke-nrhk-1-default-pool-a101b974-wfp7
5m 2m 5 {kubelet gke-nrhk-1-default-pool-a101b974-wfp7} spec.containers{fail} Normal Pulling pulling image “jerry/sap:v1.0.0”
5m 2m 5 {kubelet gke-nrhk-1-default-pool-a101b974-wfp7} spec.containers{fail} Warning Failed Failed to pull image

“jerry/sap:v1.0.0”: Error: image jerry/sap not found
5m 2m 5 {kubelet gke-nrhk-1-default-pool-a101b974-wfp7} Warning FailedSync Error syncing pod, skipping: failed to “StartContainer” for “fail” with ErrImagePull: “Error: image rosskukulinski/dne not found”

5m 11s 19 {kubelet gke-nrhk-1-default-pool-a101b974-wfp7} spec.containers{fail} Normal BackOff Back-off pulling image “rosskukulinski/dne:v1.0.0”
5m 11s 19 {kubelet gke-nrhk-1-default-pool-a101b974-wfp7} Warning FailedSync Error syncing pod, skipping: failed to “StartContainer” for “fail” with ImagePullBackOff: "Back-off pulling image “jerry/sap:v1.0.0"”

注意：观察 Pod 状态的时候，镜像缺失和仓库权限不正确是没法区分的。其它情况下，Kubernetes 将报告一个 ErrImagePull 状态。

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