在k8s集群的使用过程中，初学者可能会碰到这样的（怪异）问题： 在一个k8s集群里，部署服务（用的私有镜像仓库，如harbor）的时候，只有个别node的服务是部署成功的，其他都是部署失败的，错误的原因就是镜像拉取失败，如下： 

kubectl get pods -A -owide |grep jenkins-demo
devlopment     jenkins-demo-67d4f9d666-2fh8k            1/1     Running            0          27m     10.244.2.40     local-k8s-nd02              
devlopment     jenkins-demo-dbc9f5b6b-h78tx             0/1     ImagePullBackOff   0          6m4s    10.244.6.93     local-k8s-nd03              
production     jenkins-demo-dbc9f5b6b-tnkfs             1/1     Running            0          5m47s   10.244.2.44     local-k8s-nd02              
qatest         jenkins-demo-67d4f9d666-hb22t            1/1     Running            0          27m     10.244.2.41     local-k8s-nd02              
qatest         jenkins-demo-dbc9f5b6b-d6txr             0/1     ImagePullBackOff   0          6m      10.244.6.94     local-k8s-nd03

查看失败详情 

# kubectl describe pods -n qatest jenkins-demo-6cbfb64844-79n8l
..........
Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  78s                default-scheduler  Successfully assigned qatest/jenkins-demo-6cbfb64844-79n8l to local-k8s-nd03
  Normal   Pulling    37s (x3 over 78s)  kubelet            Pulling image "dev-hub.jiatuiyun.net/zeng/my-demo:429d9c1"
  Warning  Failed     36s (x3 over 77s)  kubelet            Failed to pull image "dev-hub.jiatuiyun.net/zeng/my-demo:429d9c1": rpc error: code = Unknown desc = Error response from daemon: pull access denied for dev-hub.jiatuiyun.net/zeng/my-demo, repository does not exist or may require docker login: denied: requested access to the resource is denied
  Warning  Failed     36s (x3 over 77s)  kubelet            Error: ErrImagePull
  Normal   BackOff    6s (x5 over 77s)   kubelet            Back-off pulling image "dev-hub.jiatuiyun.net/zeng/my-demo:429d9c1"
  Warning  Failed     6s (x5 over 77s)   kubelet            Error: ImagePullBackOff

然后我们去镜像拉取失败的机器上，直接用命令拉取，竟然是ok的 

# docker pull dev-hub.jiatuiyun.net/zeng/my-demo:eb7ec1d
eb7ec1d: Pulling from zeng/my-demo
4fe2ade4980c: Already exists 
2e793f0ebe8a: Already exists 
77995fba1918: Already exists 
4495499e856d: Already exists 
0ff8f8e34aa6: Already exists 
6c24ea7b9085: Pull complete 
c07b8e5ec47b: Pull complete 
Digest: sha256:95077089b59358820c4c763ae8bc390e470c62ac3d212abfe38292ff6389c7bb
Status: Downloaded newer image for dev-hub.jiatuiyun.net/zeng/my-demo:eb7ec1d
dev-hub.jiatuiyun.net/zeng/my-demo:eb7ec1d

同一个集群，同一个镜像仓库的同一个镜像，只是node不同而已，个别node拉取镜像ok，其余node拉取镜像失败，为何？ 其实这个问题的原因就处在，服务的部署文件里边没有配置拉取镜像用的secret，在服务配置文件中的名字是 imagePullSecrets 如下： 

.....
    spec:
      imagePullSecrets:
      - name: registry-pull-secret
      containers:
      - image: dev-hub.xxxxx.net/zeng/my-demo:
        imagePullPolicy: IfNotPresent
        name: jenkins-demo
.....

注意：如果服务分布在多个不同的namespace下，那在这些namespace下都要创建secret 至于secret如何创建就不在此赘述了，网上很多可以参考的资料。