注意：节点初始化请参考我另一个帖子 https://xwutx.cn/articles/155

1.我们需要从已有的master节点拷贝证书到需要加入的master节点上，并在新加入的节点上创建一个文件夹

1.1 需要拷贝的证书

/etc/kubernetes/pki/ca.crt
/etc/kubernetes/pki/ca.key
/etc/kubernetes/pki/sa.key
/etc/kubernetes/pki/sa.pub
/etc/kubernetes/pki/front-proxy-ca.crt
/etc/kubernetes/pki/front-proxy-ca.key
/etc/kubernetes/pki/etcd/ca.crt
/etc/kubernetes/pki/etcd/ca.key

1.2 创建文件夹

mkdir ~/.kube

2.在当前已有的master节点上运行如下命令

第一步

kubeadm init phase upload-certs --upload-certs

结果如下

I0523 23:43:01.534954   16282 version.go:256] remote version is much newer: v1.30.1; falling back to: stable-1.23
[upload-certs] Storing the certificates in Secret "kubeadm-certs" in the "kube-system" Namespace
[upload-certs] Using certificate key:
025fe85b85f335341e2a0627c0f31e1126316d5c1274ca6b3945d37c8982ec5d

第二步

kubeadm token create --print-join-command

结果如下

kubeadm join master231:6443 --token iyan57.2mf66sqmu05j0jh6 --discovery-token-ca-cert-hash sha256:bdd19b56cb053b408e20e7ccf4e0293bc5d9abb69eb8e2eb28c9c2eabc5896db

3.将得到的token和key进行拼接，得到如下命令：

kubeadm join master231:6443 --token iyan57.2mf66sqmu05j0jh6 --discovery-token-ca-cert-hash sha256:bdd19b56cb053b408e20e7ccf4e0293bc5d9abb69eb8e2eb28c9c2eabc5896db --control-plane --certificate-key 025fe85b85f335341e2a0627c0f31e1126316d5c1274ca6b3945d37c8982ec5d

注意事项：
1.不要使用 --experimental-control-plane，会报错
2.要加上--control-plane --certificate-key ，不然就会添加为node节点而不是master
3.join的时候节点上不要部署，如果部署了kubeadm reset后再join

4.join之后在原先唯一的master节点上成功后，显示如下消息：

This node has joined the cluster and a new control plane instance was created:
 
* Certificate signing request was sent to apiserver and approval was received.
* The Kubelet was informed of the new secure connection details.
* Control plane (master) label and taint were applied to the new node.
* The Kubernetes control plane instances scaled up.
* A new etcd member was added to the local/stacked etcd cluster.
 
To start administering your cluster from this node, you need to run the following as a regular user:
 
    mkdir -p $HOME/.kube
    sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
    sudo chown $(id -u):$(id -g) $HOME/.kube/config
 
Run 'kubectl get nodes' to see this node join the cluster.

这样，我们在任何一个master节点上使用命令

[root@master231~] # kubectl get nodes
NAME        STATUS   ROLES                  AGE     VERSION
master231   Ready    control-plane,master   23m     v1.23.17
master234   Ready    control-plane,master   7m45s   v1.23.17

1.第一次加入集群的时候会有以下报错：
[preflight] Running pre-flight checks

[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'

error execution phase preflight:

One or more conditions for hosting a new control plane instance is not satisfied.

unable to add a new control plane instance a cluster that doesn't have a stable controlPlaneEndpoint address

Please ensure that:

• The cluster has a stable controlPlaneEndpoint address.

• The certificates that must be shared among control plane instances are provided.

To see the stack trace of this error execute with --v=5 or higher

解决办法：

在已有的master节点查看kubeadm-config.yaml
kubectl -n kube-system get cm kubeadm-config -o yaml

发现没有controlPlaneEndpoint
添加controlPlaneEndpoint
kubectl -n kube-system edit cm kubeadm-config

大概在这么个位置：
kind: ClusterConfiguration
kubernetesVersion: v1.18.0
controlPlaneEndpoint: 10.0.0.231：6443

注意：添加的controlPlaneEndpoint改成已有master节点的地址
然后再在准备添加为master的节点上执行kubeadm join的命令