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安装环境如下：
cenos7系统
kubeadm安装方法
版本是：kubernetes1.10
K8s安装完成后，发现所有的pod都起了，除了kube-dns ,显示的状态一直是Pending.如下所示：
[root@worker3 k8s]# kubectl get pods --all-namespaces
NAMESPACE NAME READY STATUS RESTARTS AGE
kube-system etcd-worker3 1/1 Running 0 13m
kube-system kube-apiserver-worker3 1/1 Running 0 13m
kube-system kube-controller-manager-worker3 1/1 Running 0 13m
kube-system kube-dns-86f4d74b45-8ptd5 0/3 Pending 0 14m
kube-system kube-proxy-txfj4 1/1 Running 0 14m
kube-system kube-scheduler-worker3 1/1 Running 0 13m
查看 node的状态，如下所示：
[root@worker3 k8s]# kubectl get node
NAME STATUS ROLES AGE VERSION
worker3 NotReady master 14m v1.10.0
查看日志如下所示：
[root@worker3 k8s]# journalctl -f -u kubelet.service
-- Logs begin at Mon 2018-09-17 07:17:54 EDT. --
Sep 20 02:03:47 worker3 kubelet[27492]: W0920 02:03:47.950864 27492 cni.go:171] Unable to update cni config: No networks found in /etc/cni/net.d
Sep 20 02:03:47 worker3 kubelet[27492]: E0920 02:03:47.951056 27492 kubelet.go:2125] Container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni config uninitialized
Sep 20 02:03:52 worker3 kubelet[27492]: W0920 02:03:52.952334 27492 cni.go:171] Unable to update cni config: No networks found in /etc/cni/net.d
Sep 20 02:03:52 worker3 kubelet[27492]: E0920 02:03:52.952519 27492 kubelet.go:2125] Container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni config uninitialized
解决的方法：
创建 flannel的pod，，命令如下：
kubectl create -f https://raw.githubusercontent.com/coreos/flannel/v0.9.1/Documentation/kube-flannel.yml等一会儿，发现 pod以及node都正常了。
参考文档
http://www.winseliu.com/blog/2017/08/13/kubeadm-install-k8s-on-centos7-with-resources/
https://tachingchen.com/tw/blog/kubernetes-installation-with-kubeadm/