书籍来源：《CKA/CKAD应试指南：从Docker到Kubernetes完全攻略》

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有一点需要注意，在kubernetes集群安装好之后，kubectl命令都是在master上执行的。在敲命令时发现，kubectl后面的子命令如果能执行Tab键，会带来极大的便捷性，但是默认却是不能使用Tab键的，需要设置一下。

步骤1：编辑/etc/profile，在第二行加上source <(kubectl completion bash)并使之生效。

##########实操验证##########
[root@vms10 ~]# head -3 /etc/profile
# /etc/profile
source <(kubectl completion bash)
# System wide environment and startup programs, for login setup
[root@vms10 ~]#
[root@vms10 ~]# source /etc/profile
[root@vms10 ~]# 

注意1：要让此设置生效的话，操作系统需要安装bash-completion。

注意2：这里的小括号是英文版的小括号，很多人的默认输入法是中文输入法，这里很容把小括号敲成了中文的小括号。

因为后期可能要复制yaml格式的内容，所以设置编辑器vim的属性。

步骤2：创建/root/.vimrc内容如下所示。

##########实操验证##########
[root@vms10 ~]# cat .vimrc 
set paste
[root@vms10 ~]# 

删除节点及重新加入

有时我们需要把kubernetes里的某个节点移除，重新添加其他节点。把节点加入集群的方法前面已经讲了，但是要把节点从集群中移除该如何操作呢？下面演示如何把vms12.rhce.cc从集群中删除。

步骤1：把vms12.rhce.cc设置为维护模式。

通过命令kubectl drain把节点设置为维护模式，会把已经在此节点上运行的pod驱逐到其点上运行。

##########实操验证##########
[root@vms10 ~]# kubectl drain vms12.rhce.cc --delete-emptydir-data --force --ignore-daemonsets 
node/vms12.rhce.cc cordoned
WARNING: ignoring DaemonSet-managed Pods: kube-system/calico-node-zhqzd, kube-system/kube-proxy-d4wgd
evicting pod kube-system/coredns-545d6fc579-8bwgg
evicting pod kube-system/calico-kube-controllers-7cc8dd57d9-nj9gl
evicting pod kube-system/coredns-545d6fc579-6hzdn
pod/calico-kube-controllers-7cc8dd57d9-nj9gl evicted
pod/coredns-545d6fc579-8bwgg evicted
pod/coredns-545d6fc579-6hzdn evicted
node/vms12.rhce.cc evicted
[root@vms10 ~]# 

步骤2：删除这个节点。

##########实操验证##########
[root@vms10 ~]# kubectl delete node vms12.rhce.cc 
node "vms12.rhce.cc" deleted
[root@vms10 ~]# 
[root@vms10 ~]# kubectl get nodes
NAME            STATUS   ROLES                  AGE   VERSION
vms10.rhce.cc   Ready    control-plane,master   25m   v1.21.1
vms11.rhce.cc   Ready    <none>                 24m   v1.21.1
[root@vms10 ~]# 

步骤3：清空节点上的配置。

再次把vms12.rhce.cc加入集群，先用kubeadm reset清除vms12上kubernetes的设置。

##########实操验证##########
[root@vms12 ~]# 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
W0504 11:31:17.165737   20309 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 /var/lib/dockershim /var/run/kubernetes /var/lib/cni]

The reset process does not clean CNI configuration. To do so, you must remove /etc/cni/net.d

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 by using the "iptables" command.

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.
[root@vms12 ~]# 

步骤4：重新加入集群。

##########实操验证##########
[root@vms12 ~]# kubeadm join 192.168.1.110:6443 --token zryqi2.7r0c6qxkp9wr4awz \
>         --discovery-token-ca-cert-hash sha256:e52d78693299a9a9a177b2223cb8688c11650f5d8f9311c5461545355dd86692 
 [preflight] Running pre-flight checks
        [WARNING IsDockerSystemdCheck]: detected "cgroupfs" as the Docker cgroup driver. The recommended driver is "systemd". Please follow the guide at https://kubernetes.io/docs/setup/cri/
        [WARNING SystemVerification]: this Docker version is not on the list of validated versions: 23.0.5. Latest validated version: 20.10
[preflight] Reading configuration from the cluster...
[preflight] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[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] Starting the kubelet
[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.

[root@vms12 ~]#  

注意1：不管是master还是worker，如果想清空kubernetes设置的话，需要执行kubeadm reset命令。

注意2：如果再次加入集群时出错的话，只要把/etc/kubernetes/pki/和/var/lib/kubelet/两个目录的内容清空，然后再次加入集群即可。记住是删除这两个目录里的内容，不是删除这两个目录。

3.3.2 常见的一些命令

本节讲述一些在kubernetes里常能用到的查看集群信息的命令。

1. 查看kubernetes集群信息

##########实操验证##########
[root@vms10 ~]# kubectl cluster-info
Kubernetes control plane is running at https://192.168.1.110:6443
CoreDNS is running at https://192.168.1.110:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
[root@vms10 ~]# 

2. 查看kubernetes版本

##########实操验证##########
[root@vms10 ~]# kubectl version
Client Version: version.Info{Major:"1", Minor:"21", GitVersion:"v1.21.1", GitCommit:"5e58841cce77d4bc13713ad2b91fa0d961e69192", GitTreeState:"clean", BuildDate:"2021-05-12T14:18:45Z", GoVersion:"go1.16.4", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"21", GitVersion:"v1.21.1", GitCommit:"5e58841cce77d4bc13713ad2b91fa0d961e69192", GitTreeState:"clean", BuildDate:"2021-05-12T14:12:29Z", GoVersion:"go1.16.4", Compiler:"gc", Platform:"linux/amd64"}
[root@vms10 ~]# 

如果要看精简的信息，可以加上--short选项。

##########实操验证##########
[root@vms10 ~]# kubectl version --short
Client Version: v1.21.1
Server Version: v1.21.1
[root@vms10 ~]# 

3. 查看kubernetes里所支持的api-version（后面章节会遇到）

##########实操验证##########
[root@vms10 ~]# kubectl api-versions
admissionregistration.k8s.io/v1
admissionregistration.k8s.io/v1beta1
apiextensions.k8s.io/v1
apiextensions.k8s.io/v1beta1
apiregistration.k8s.io/v1
apiregistration.k8s.io/v1beta1
apps/v1
authentication.k8s.io/v1
authentication.k8s.io/v1beta1
authorization.k8s.io/v1
authorization.k8s.io/v1beta1
autoscaling/v1
autoscaling/v2beta1
autoscaling/v2beta2
batch/v1
batch/v1beta1
certificates.k8s.io/v1
certificates.k8s.io/v1beta1
coordination.k8s.io/v1
coordination.k8s.io/v1beta1
crd.projectcalico.org/v1
discovery.k8s.io/v1
discovery.k8s.io/v1beta1
events.k8s.io/v1
events.k8s.io/v1beta1
extensions/v1beta1
flowcontrol.apiserver.k8s.io/v1beta1
networking.k8s.io/v1
networking.k8s.io/v1beta1
node.k8s.io/v1
node.k8s.io/v1beta1
policy/v1
policy/v1beta1
rbac.authorization.k8s.io/v1
rbac.authorization.k8s.io/v1beta1
scheduling.k8s.io/v1
scheduling.k8s.io/v1beta1
storage.k8s.io/v1
storage.k8s.io/v1beta1
v1
[root@vms10 ~]#