9.2、镜像拉取策略（imagePullPolicy）

创建 pod-imagepullpolicy.yaml 文件，内容如下：

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apiVersion: v1
kind: Pod
metadata:
  name: pod-imagepullpolicy
  namespace: dev
spec:
  containers:
  - name: nginx
    image: nginx:1.17.1
    imagePullPolicy: Never # 用于设置镜像拉取策略
  - name: busybox
    image: registry.cn-hangzhou.aliyuncs.com/zznn/mycentos:busybox-1.30 # busybox:1.30

imagePullPolicy，用于设置镜像拉取策略，kubernetes支持配置三种拉取策略：

  • Always：总是从远程仓库拉取镜像（一直远程下载）
  • IfNotPresent：本地有则使用本地镜像，本地没有则从远程仓库拉取镜像（本地有就本地 本地没远程下载）
  • Never：只使用本地镜像，从不去远程仓库拉取，本地没有就报错 （一直使用本地）

默认值说明：

如果镜像tag为具体版本号， 默认策略是：IfNotPresent

如果镜像tag为：latest（最终版本） ，默认策略是always

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# 创建Pod
[root@k8s-master01 pod]# kubectl create -f pod-imagepullpolicy.yaml
pod/pod-imagepullpolicy created

# 查看Pod详情
# 此时明显可以看到nginx镜像有一步Pulling image "nginx:1.17.1"的过程
[root@k8s-master01 pod]# kubectl describe pod pod-imagepullpolicy -n dev
......
Events:
  Type     Reason     Age               From               Message
  ----     ------     ----              ----               -------
  Normal   Scheduled  <unknown>         default-scheduler  Successfully assigned dev/pod-imagePullPolicy to node1
  Normal   Pulling    32s               kubelet, node1     Pulling image "nginx:1.17.1"
  Normal   Pulled     26s               kubelet, node1     Successfully pulled image "nginx:1.17.1"
  Normal   Created    26s               kubelet, node1     Created container nginx
  Normal   Started    25s               kubelet, node1     Started container nginx
  Normal   Pulled     7s (x3 over 25s)  kubelet, node1     Container image "busybox:1.30" already present on machine
  Normal   Created    7s (x3 over 25s)  kubelet, node1     Created container busybox
  Normal   Started    7s (x3 over 25s)  kubelet, node1     Started container busybox