节点kubeadm join 时发现kubelet启动失败，no route to host 清除iptables规则，关闭防火墙即可

 kubeadm join 10.40.19.85:6443 --token 8g02qu.h37najizohm2hi5s     --discovery-token-ca-cert-hash sha256:22a48d5cd38c60e4103c1a449dd684247186fba4d4b939f0332eebf31b441952
[preflight] Running pre-flight checks
---没有反应---

查看日志
[root@uat-n1 kube]# journalctl -f -u kubelet
-- Logs begin at Fri 2019-12-13 04:22:52 CST. --
Dec 13 05:24:41 uat-n1 systemd[1]: Unit kubelet.service entered failed state.
Dec 13 05:24:41 uat-n1 systemd[1]: kubelet.service failed.
Dec 13 05:24:51 uat-n1 systemd[1]: kubelet.service holdoff time over, scheduling restart.
Dec 13 05:24:51 uat-n1 systemd[1]: Stopped kubelet: The Kubernetes Node Agent.
Dec 13 05:24:51 uat-n1 systemd[1]: Started kubelet: The Kubernetes Node Agent.
Dec 13 05:24:54 uat-n1 kubelet[16121]: F1213 05:24:54.254563   16121 server.go:193] failed to load Kubelet config file /var/lib/kubelet/config.yaml, error failed to read kubelet config file "/var/lib/kubelet/config.yaml", error: open /var/lib/kubelet/config.yaml: no such file or directory
Dec 13 05:24:54 uat-n1 systemd[1]: kubelet.service: main process exited, code=exited, status=255/n/a

查看master，发现coredns没有running起来

[root@uat-m ttebdadmin]# kubectl get pods -o wide -A -w
NAMESPACE     NAME                            READY   STATUS             RESTARTS   AGE   IP            NODE    NOMINATED NODE   READINESS GATES
kube-system   coredns-fb8b8dccf-28xlr         0/1     CrashLoopBackOff   2          12h   10.244.0.2    uat-m              
kube-system   coredns-fb8b8dccf-7v88v         0/1     CrashLoopBackOff   1          12h   10.244.0.3    uat-m              
kube-system   etcd-uat-m                      1/1     Running            2          12h   10.40.19.85   uat-m              
kube-system   kube-apiserver-uat-m            1/1     Running            2          12h   10.40.19.85   uat-m              
kube-system   kube-controller-manager-uat-m   1/1     Running            2          12h   10.40.19.85   uat-m              
kube-system   kube-flannel-ds-amd64-hmwdm     1/1     Running            0          78s   10.40.19.85   uat-m              
kube-system   kube-proxy-ddppl                1/1     Running            2          12h   10.40.19.85   uat-m              
kube-system   kube-scheduler-uat-m            1/1     Running            2          12h   10.40.19.85   uat-m              
^C[root@uat-m ttebdadmin]# kubectl logs -n kube-system coredns-fb8b8dccf-28xlr
E1213 13:27:24.280028       1 reflector.go:134] github.com/coredns/coredns/plugin/kubernetes/controller.go:317: Failed to list *v1.Endpoints: Get https://10.1.0.1:443/api/v1/endpoints?limit=500&resourceVersion=0: dial tcp 10.1.0.1:443: connect: no route to host
E1213 13:27:24.280028       1 reflector.go:134] github.com/coredns/coredns/plugin/kubernetes/controller.go:317: Failed to list *v1.Endpoints: Get https://10.1.0.1:443/api/v1/endpoints?limit=500&resourceVersion=0: dial tcp 10.1.0.1:443: connect: no route to host
log: exiting because of error: log: cannot create log: open /tmp/coredns.coredns-fb8b8dccf-28xlr.unknownuser.log.ERROR.20191213-132724.1: no such file or directory

发现错误是connect: no route to host

清除iptables规则即可
在master上运行

systemctl stop kubelet
systemctl stop docker
iptables --flush
iptables -tnat --flush
systemctl start kubelet
systemctl start docker