k8s node节点重新加入master集群的实现

1、删除node节点

执行kubectl delete node node01

2、这时如果直接执行加入，会报错。如下：

[root@k8s-node02 pki]# kubeadm join 192.168.140.128:6443 --token abcdef.0123456789abcdef   --discovery-token-ca-cert-hash sha256:a3d9827be411208258aea7f3ee9aa396956c0a77c8b570503dd677aa3b6eb6d8
[preflight] Running pre-flight checks
 [WARNING SystemVerification]: this Docker version is not on the list of validated versions: 19.03.12. Latest validated version: 18.09
error execution phase preflight: [preflight] Some fatal errors occurred:
 [ERROR FileAvailable--etc-kubernetes-kubelet.conf]: /etc/kubernetes/kubelet.conf already exists
 [ERROR FileAvailable--etc-kubernetes-bootstrap-kubelet.conf]: /etc/kubernetes/bootstrap-kubelet.conf already exists
 [ERROR Port-10250]: Port 10250 is in use
 [ERROR FileAvailable--etc-kubernetes-pki-ca.crt]: /etc/kubernetes/pki/ca.crt already exists
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`

解决方案：

根据报错可以看到端口被占用，配置文件可ca证书已经生成，所以需要删除这些配置文件和证书，并且kill掉占用的端口。建议删除之前先备份。

[root@k8s-node02 pki]# lsof -i:10250
COMMAND PID USER  FD  TYPE DEVICE SIZE/OFF NODE NAME
kubelet 694 root  30u IPv6 26021   0t0 TCP *:10250 (LISTEN)
[root@k8s-node02 pki]# kill -9 694
[root@k8s-node02 pki]# cd /etc/kubernetes/
[root@k8s-node02 kubernetes]# ls
bootstrap-kubelet.conf kubelet.conf manifests pki
[root@k8s-node02 kubernetes]# mv bootstrap-kubelet.conf bootstrap-kubelet.conf_bk
[root@k8s-node02 kubernetes]# mv kubelet.conf kubelet.conf_bk
[root@k8s-node02 kubernetes]# cd pki/
[root@k8s-node02 pki]# ls
ca.crt
[root@k8s-node02 pki]# rm -rf ca.crt

3、再次执行加入，又出现报错。

[root@k8s-node02 ~]# kubeadm join 192.168.140.128:6443 --token abcdef.0123456789abcdef   --discovery-token-ca-cert-hash sha256:a3d9827be411208258aea7f3ee9aa396956c0a77c8b570503dd677aa3b6eb6d8
[preflight] Running pre-flight checks
 [WARNING SystemVerification]: this Docker version is not on the list of validated versions: 19.03.12. Latest validated version: 18.09
[preflight] Reading configuration from the cluster...
[preflight] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'
[kubelet-start] Downloading configuration for the kubelet from the "kubelet-config-1.15" ConfigMap in the kube-system namespace
[kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[kubelet-start] Activating the kubelet service
[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap...
[kubelet-check] Initial timeout of 40s passed.
error execution phase kubelet-start: error uploading crisocket: timed out waiting for the condition

解决方案：

执行kubeadm reset子节点重置

[root@k8s-node02 ~]# kubeadm reset
[reset] WARNING: Changes made to this host by 'kubeadm init' or 'kubeadm join' will be reverted.
[reset] Are you sure you want to proceed? [y/N]: y
[preflight] Running pre-flight checks
W0710 10:22:57.487306  31093 removeetcdmember.go:79] [reset] No kubeadm config, using etcd pod spec to get data directory
[reset] No etcd config found. Assuming external etcd
[reset] Please, manually reset etcd to prevent further issues
[reset] Stopping the kubelet service
[reset] Unmounting mounted directories in "/var/lib/kubelet"
[reset] Deleting contents of config directories: [/etc/kubernetes/manifests /etc/kubernetes/pki]
[reset] Deleting files: [/etc/kubernetes/admin.conf /etc/kubernetes/kubelet.conf /etc/kubernetes/bootstrap-kubelet.conf /etc/kubernetes/controller-manager.conf /etc/kubernetes/scheduler.conf]
[reset] Deleting contents of stateful directories: [/var/lib/kubelet /etc/cni/net.d /var/lib/dockershim /var/run/kubernetes]

The reset process does not reset or clean up iptables rules or IPVS tables.
If you wish to reset iptables, you must do so manually.
For example:
iptables -F && iptables -t nat -F && iptables -t mangle -F && iptables -X

If your cluster was setup to utilize IPVS, run ipvsadm --clear (or similar)
to reset your system's IPVS tables.

The reset process does not clean your kubeconfig files and you must remove them manually.
Please, check the contents of the $HOME/.kube/config file.

4、最后执行加入，问题解决。

[root@k8s-node02 ~]# kubeadm join 192.168.140.128:6443 --token abcdef.0123456789abcdef   --discovery-token-ca-cert-hash sha256:a3d9827be411208258aea7f3ee9aa396956c0a77c8b570503dd677aa3b6eb6d8
[preflight] Running pre-flight checks
 [WARNING SystemVerification]: this Docker version is not on the list of validated versions: 19.03.12. Latest validated version: 18.09
[preflight] Reading configuration from the cluster...
[preflight] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'
[kubelet-start] Downloading configuration for the kubelet from the "kubelet-config-1.15" ConfigMap in the kube-system namespace
[kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[kubelet-start] Activating the kubelet service
[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap...

This node has joined the cluster:
* Certificate signing request was sent to apiserver and a response was received.
* The Kubelet was informed of the new secure connection details.

Run 'kubectl get nodes' on the control-plane to see this node join the cluster.

5、查看master节点，加入成功。

[root@k8s-master01 ~]# kubectl get nodes
NAME      STATUS  ROLES  AGE  VERSION
k8s-master01  Ready  master  120m  v1.15.1
k8s-node01   Ready  <none>  100m  v1.15.1
k8s-node02   Ready  <none>  83m  v1.15.1

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