kubernetes创建pod出现ImagePullBackOff，是describe查看，如下信息：

kubectl describe pods -n rook-ceph-system rook-ceph-operator-6b4c5d4684-q4sl4
Name:               rook-ceph-operator-6b4c5d4684-q4sl4
Namespace:          rook-ceph-system
Priority:           0
PriorityClassName:  <none>
Node:               node3/192.168.2.218
Start Time:         Sun, 20 Jan 2019 05:12:47 +0800
Labels:             app=rook-ceph-operator
                    pod-template-hash=2607180240
Annotations:        <none>
Status:             Pending
IP:                 10.244.3.18
Controlled By:      ReplicaSet/rook-ceph-operator-6b4c5d4684
Containers:
  rook-ceph-operator:
    Container ID:  
    Image:         rook/ceph:master
    Image ID:      
    Port:          <none>
    Host Port:     <none>
    Args:
      ceph
      operator
    State:          Waiting
      Reason:       ImagePullBackOff
    Ready:          False
    Restart Count:  0
    Environment:
      ROOK_ALLOW_MULTIPLE_FILESYSTEMS:    false
      ROOK_LOG_LEVEL:                     INFO
      ROOK_MON_HEALTHCHECK_INTERVAL:      45s
      ROOK_MON_OUT_TIMEOUT:               300s
      ROOK_DISCOVER_DEVICES_INTERVAL:     60m
      ROOK_HOSTPATH_REQUIRES_PRIVILEGED:  false
      ROOK_ENABLE_SELINUX_RELABELING:     true
      ROOK_ENABLE_FSGROUP:                true
      NODE_NAME:                           (v1:spec.nodeName)
      POD_NAME:                           rook-ceph-operator-6b4c5d4684-q4sl4 (v1:metadata.name)
      POD_NAMESPACE:                      rook-ceph-system (v1:metadata.namespace)
    Mounts:
      /etc/ceph from default-config-dir (rw)
      /var/lib/rook from rook-config (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from rook-ceph-system-token-hsb47 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             False 
  ContainersReady   False 
  PodScheduled      True 
Volumes:
  rook-config:
    Type:    EmptyDir (a temporary directory that shares a pod's lifetime)
    Medium:  
  default-config-dir:
    Type:    EmptyDir (a temporary directory that shares a pod's lifetime)
    Medium:  
  rook-ceph-system-token-hsb47:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  rook-ceph-system-token-hsb47
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type     Reason          Age              From               Message
  ----     ------          ----             ----               -------
  Normal   Scheduled       4m               default-scheduler  Successfully assigned rook-ceph-system/rook-ceph-operator-6b4c5d4684-q4sl4 to node3
  Warning  Failed          4m               kubelet, node3     Failed to pull image "rook/ceph:master": rpc error: code = Unknown desc = error pulling image configuration: Get https://production.cloudflare.docker.com/registry-v2/docker/registry/v2/blobs/sha256/6a/6a24edf782ca5648a502bf81f368e3b1ba92988e733d72e2cf9025cac89903e1/data?verify=1549257241-9PpxfOCv75gYTQrP8VCjoqeYVnI%3D: x509: certificate has expired or is not yet valid
  Normal   SandboxChanged  4m               kubelet, node3     Pod sandbox changed, it will be killed and re-created.
  Warning  Failed          3m               kubelet, node3     Failed to pull image "rook/ceph:master": rpc error: code = Unknown desc = error pulling image configuration: Get https://production.cloudflare.docker.com/registry-v2/docker/registry/v2/blobs/sha256/6a/6a24edf782ca5648a502bf81f368e3b1ba92988e733d72e2cf9025cac89903e1/data?verify=1549257257-2PNM%2FFH5sUvEf1OU4hxgU0aI3%2Bw%3D: x509: certificate has expired or is not yet valid
  Warning  Failed          3m               kubelet, node3     Failed to pull image "rook/ceph:master": rpc error: code = Unknown desc = error pulling image configuration: Get https://production.cloudflare.docker.com/registry-v2/docker/registry/v2/blobs/sha256/6a/6a24edf782ca5648a502bf81f368e3b1ba92988e733d72e2cf9025cac89903e1/data?verify=1549257290-ejyauPSi7E8OB9WDBixNDtyLivU%3D: x509: certificate has expired or is not yet valid
  Normal   Pulling         2m (x4 over 4m)  kubelet, node3     pulling image "rook/ceph:master"
  Warning  Failed          2m (x4 over 4m)  kubelet, node3     Error: ErrImagePull
  Warning  Failed          2m               kubelet, node3     Failed to pull image "rook/ceph:master": rpc error: code = Unknown desc = error pulling image configuration: Get https://production.cloudflare.docker.com/registry-v2/docker/registry/v2/blobs/sha256/6a/6a24edf782ca5648a502bf81f368e3b1ba92988e733d72e2cf9025cac89903e1/data?verify=1549257336-%2Bd5Xd%2FOj0i9nrmnOWbHkGjv30Yw%3D: x509: certificate has expired or is not yet valid
  Normal   BackOff         2m (x6 over 3m)  kubelet, node3     Back-off pulling image "rook/ceph:master"
  Warning  Failed          2m (x6 over 3m)  kubelet, node3     Error: ImagePullBackOff