今天使用kubectl命令查看pod信息时，一直正常运行的k8s集群突然不能访问了，输入任何命令都提示以下报错：
Unable to connect to the server: x509: certificate has expired or is not yet valid: current time 2025-01-25T11:35:45+08:00 is after 2024-11-22T23:44:48Z

解决方案：

参考官方文档： kubeadm证书管理 使用命令kubeadm alpha certs 来管理证书：

1. 使用命令kubeadm alpha certs renew all更新证书，返回

[renew] Reading configuration from the cluster...
[renew] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'

certificate embedded in the kubeconfig file for the admin to use and for kubeadm itself renewed
certificate for serving the Kubernetes API renewed
certificate the apiserver uses to access etcd renewed
certificate for the API server to connect to kubelet renewed
certificate embedded in the kubeconfig file for the controller manager to use renewed
certificate for liveness probes to healthcheck etcd renewed
certificate for etcd nodes to communicate with each other renewed
certificate for serving etcd renewed
certificate for the front proxy client renewed
certificate embedded in the kubeconfig file for the scheduler manager to use renewed

2. 使用如下命令拷贝新生成的配置文件

sudo kubeadm alpha kubeconfig user --client-name=admin --org=system:masters > /tmp/admin.conf
sudo cp /tmp/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config

3. 重启kubeletsystemctl restart kubelet 即可正常使用K8S集群

[root@k8smaster k8s]# kubectl get po
NAME                             READY   STATUS      RESTARTS   AGE
cron-job-test-1732318920-k2g76   0/1     Completed   0          63d
cron-job-test-1732318980-kcr4x   0/1     Completed   0          63d
cron-job-test-1732319040-b88rf   0/1     Completed   0          63d

4. 再次查看证书到期情况

[root@k8smaster k8s]# kubeadm alpha certs check-expiration
[check-expiration] Reading configuration from the cluster...
[check-expiration] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'

CERTIFICATE                EXPIRES                  RESIDUAL TIME   CERTIFICATE AUTHORITY   EXTERNALLY MANAGED
admin.conf                 Jan 25, 2026 05:55 UTC   364d                                    no
apiserver                  Jan 25, 2026 05:55 UTC   364d            ca                      no
apiserver-etcd-client      Jan 25, 2026 05:55 UTC   364d            etcd-ca                 no
apiserver-kubelet-client   Jan 25, 2026 05:55 UTC   364d            ca                      no
controller-manager.conf    Jan 25, 2026 05:55 UTC   364d                                    no
etcd-healthcheck-client    Jan 25, 2026 05:55 UTC   364d            etcd-ca                 no
etcd-peer                  Jan 25, 2026 05:55 UTC   364d            etcd-ca                 no
etcd-server                Jan 25, 2026 05:55 UTC   364d            etcd-ca                 no
front-proxy-client         Jan 25, 2026 05:55 UTC   364d            front-proxy-ca          no
scheduler.conf             Jan 25, 2026 05:55 UTC   364d                                    no

CERTIFICATE AUTHORITY   EXPIRES                  RESIDUAL TIME   EXTERNALLY MANAGED
ca                      Nov 20, 2033 23:44 UTC   8y              no
etcd-ca                 Nov 20, 2033 23:44 UTC   8y              no
front-proxy-ca          Nov 20, 2033 23:44 UTC   8y              no

注意事项：

官网上给的命令是kubeadm certs check-expiration，标识的k8s版本是V1.15，直接在本地执行该命令报错：

[root@k8smaster k8s]# kubeadm certs check-expiration
unknown command "certs" for "kubeadm"
To see the stack trace of this error execute with --v=5 or higher

查了下，我本地的k8s版本是1.19，certs命令放在了 kubeadm alpha下，需要将kubeadm certs 替换为 kubeadm aplha certs 执行即可

[root@k8smaster k8sh]# kubeadm version
kubeadm version: &version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.5", GitCommit:"e338cf2c6d297aa603b50ad3a301f761b4173aa6", GitTreeState:"clean", BuildDate:"2020-12-09T11:16:40Z", GoVersion:"go1.15.2", Compiler:"gc", Platform:"linux/amd64"}

[root@k8smaster k8s]# kubeadm --help


    ┌──────────────────────────────────────────────────────────┐
    │ KUBEADM                                                  │
    │ Easily bootstrap a secure Kubernetes cluster             │
    │                                                          │
    │ Please give us feedback at:                              │
    │ https://github.com/kubernetes/kubeadm/issues             │
    └──────────────────────────────────────────────────────────┘

Example usage:

    Create a two-machine cluster with one control-plane node
    (which controls the cluster), and one worker node
    (where your workloads, like Pods and Deployments run).

    ┌──────────────────────────────────────────────────────────┐
    │ On the first machine:                                    │
    ├──────────────────────────────────────────────────────────┤
    │ control-plane# kubeadm init                              │
    └──────────────────────────────────────────────────────────┘

    ┌──────────────────────────────────────────────────────────┐
    │ On the second machine:                                   │
    ├──────────────────────────────────────────────────────────┤
    │ worker# kubeadm join <arguments-returned-from-init>      │
    └──────────────────────────────────────────────────────────┘

    You can then repeat the second step on as many other machines as you like.

Usage:
  kubeadm [command]

Available Commands:
  alpha       Kubeadm experimental sub-commands
  completion  Output shell completion code for the specified shell (bash or zsh)
  config      Manage configuration for a kubeadm cluster persisted in a ConfigMap in the                   cluster
  help        Help about any command
  init        Run this command in order to set up the Kubernetes control plane
  join        Run this on any machine you wish to join an existing cluster
  reset       Performs a best effort revert of changes made to this host by 'kubeadm init                  ' or 'kubeadm join'
  token       Manage bootstrap tokens
  upgrade     Upgrade your cluster smoothly to a newer version with this command
  version     Print the version of kubeadm

Flags:
      --add-dir-header           If true, adds the file directory to the header of the lo                  g messages
  -h, --help                     help for kubeadm
      --log-file string          If non-empty, use this log file
      --log-file-max-size uint   Defines the maximum size a log file can grow to. Unit is                   megabytes. If the value is 0, the maximum file size is unlimited. (default 1800)
      --rootfs string            [EXPERIMENTAL] The path to the 'real' host root filesyst                  em.
      --skip-headers             If true, avoid header prefixes in the log messages
      --skip-log-headers         If true, avoid headers when opening log files
  -v, --v Level                  number for the log level verbosity

Use "kubeadm [command] --help" for more information about a command.
[root@k8smaster k8s]# kubectl alpha --help
These commands correspond to alpha features that are not enabled in Kubernetes
clusters by default.

Available Commands:
  debug       Attach a debug container to a running pod

Use "kubectl <command> --help" for more information about a given command.
[root@k8smaster k8s]# kubeadm alpha --help
Kubeadm experimental sub-commands

Usage:
  kubeadm alpha [command]

Available Commands:
  certs       Commands related to handling kubernetes certificates
  kubeconfig  Kubeconfig file utilities
  selfhosting Make a kubeadm cluster self-hosted

Flags:
  -h, --help   help for alpha

Global Flags:
      --add-dir-header           If true, adds the file directory to the header of the log messages
      --log-file string          If non-empty, use this log file
      --log-file-max-size uint   Defines the maximum size a log file can grow to. Unit is megabytes. If the value is 0, the maximum file size is unlimited. (default 1800)
      --rootfs string            [EXPERIMENTAL] The path to the 'real' host root filesystem.
      --skip-headers             If true, avoid header prefixes in the log messages
      --skip-log-headers         If true, avoid headers when opening log files
  -v, --v Level                  number for the log level verbosity

Additional help topics:
  kubeadm alpha phase Invoke subsets of kubeadm functions separately for a manual install

Use "kubeadm alpha [command] --help" for more information about a command.