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This script can renew kubernetes cluster certificates that have expired or are about to expire.

This script can renew any version's k8s cluster certificate (clusters initialized with kubeadm)

The certificates that generated by kubeadm are valid for only 1 year. This script can extend that duration to 10 years.

This script only handles master node's certificates. Kubelet certificates of worker nodes will be renewed automatically.

1. Usage

  • Only to renew master nodes' certificate if etcd doesn't has certificate. See this (etcd doesn't use TLS encrypted connection by default if the k8s version is less than v1.9.x)

  • Use the following steps to renew otherwise:

1.1 Download the script

git clone https://github.com/yuyicai/update-kube-cert.git
cd update-kube-cert
chmod 755 update-kubeadm-cert.sh

1.2 Renew the certificate

If you use containerd as CRI runtime：

  • add the --cri containerd argument when executing the script. The default is docker runtime.
  • manual restart the control plane Pods (necessary)

    After running the command you should restart the control plane Pods. This is required since dynamic certificate reload is currently not supported for all components and certificates. Static Pods are managed by the local kubelet and not by the API Server, thus kubectl cannot be used to delete and restart them. To restart a static Pod you can temporarily remove its manifest file from /etc/kubernetes/manifests/ and wait for 20 seconds (see the fileCheckFrequency value in KubeletConfiguration struct. The kubelet will terminate the Pod if it's no longer in the manifest directory. You can then move the file back and after another fileCheckFrequency period, the kubelet will recreate the Pod and the certificate renewal for the component can complete.
    https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-certs/#manual-certificate-renewal

Use ./update-kubeadm-cert.sh all or bash update-kubeadm-cert.sh all to execute it. Please do not use sh update-kubeadm-cert.sh all，Because some of Linux distributions doesn't link sh to bash. it may cause the problem of compatibility.

Execute on every master node if the cluster has more than one

./update-kubeadm-cert.sh all --cri docker

The output should be like this:

CERTIFICATE                                       EXPIRES
/etc/kubernetes/controller-manager.config         Sep 12 08:38:56 2022 GMT
/etc/kubernetes/scheduler.config                  Sep 12 08:38:56 2022 GMT
/etc/kubernetes/admin.config                      Sep 12 08:38:56 2022 GMT
/etc/kubernetes/pki/ca.crt                        Sep 11 08:38:53 2031 GMT
/etc/kubernetes/pki/apiserver.crt                 Sep 12 08:38:54 2022 GMT
/etc/kubernetes/pki/apiserver-kubelet-client.crt  Sep 12 08:38:54 2022 GMT
/etc/kubernetes/pki/front-proxy-ca.crt            Sep 11 08:38:54 2031 GMT
/etc/kubernetes/pki/front-proxy-client.crt        Sep 12 08:38:54 2022 GMT
/etc/kubernetes/pki/etcd/ca.crt                   Sep 11 08:38:55 2031 GMT
/etc/kubernetes/pki/etcd/server.crt               Sep 12 08:38:55 2022 GMT
/etc/kubernetes/pki/etcd/peer.crt                 Sep 12 08:38:55 2022 GMT
/etc/kubernetes/pki/etcd/healthcheck-client.crt   Sep 12 08:38:55 2022 GMT
/etc/kubernetes/pki/apiserver-etcd-client.crt     Sep 12 08:38:56 2022 GMT
[2021-09-12T16:41:25.93+0800][INFO] backup /etc/kubernetes to /etc/kubernetes.old-20210912
[2021-09-12T16:41:25.93+0800][INFO] updating...
[2021-09-12T16:41:25.99+0800][INFO] updated /etc/kubernetes/pki/etcd/server.conf
[2021-09-12T16:41:26.04+0800][INFO] updated /etc/kubernetes/pki/etcd/peer.conf
[2021-09-12T16:41:26.07+0800][INFO] updated /etc/kubernetes/pki/etcd/healthcheck-client.conf
[2021-09-12T16:41:26.11+0800][INFO] updated /etc/kubernetes/pki/apiserver-etcd-client.conf
[2021-09-12T16:41:26.54+0800][INFO] restarted etcd with docker
[2021-09-12T16:41:26.60+0800][INFO] updated /etc/kubernetes/pki/apiserver.crt
[2021-09-12T16:41:26.64+0800][INFO] updated /etc/kubernetes/pki/apiserver-kubelet-client.crt
[2021-09-12T16:41:26.69+0800][INFO] updated /etc/kubernetes/controller-manager.conf
[2021-09-12T16:41:26.74+0800][INFO] updated /etc/kubernetes/scheduler.conf
[2021-09-12T16:41:26.79+0800][INFO] updated /etc/kubernetes/admin.conf
[2021-09-12T16:41:26.79+0800][INFO] backup /root/.kube/config to /root/.kube/config.old-20210912
[2021-09-12T16:41:26.80+0800][INFO] copy the admin.conf to /root/.kube/config
[2021-09-12T16:41:26.85+0800][INFO] updated /etc/kubernetes/kubelet.conf
[2021-09-12T16:41:26.88+0800][INFO] updated /etc/kubernetes/pki/front-proxy-client.crt
[2021-09-12T16:41:28.70+0800][INFO] restarted apiserver with docker
[2021-09-12T16:41:29.17+0800][INFO] restarted controller-manager with docker
[2021-09-12T16:41:30.07+0800][INFO] restarted scheduler with docker
[2021-09-12T16:41:30.13+0800][INFO] restarted kubelet
[2021-09-12T16:41:30.14+0800][INFO] done!!!
CERTIFICATE                                       EXPIRES
/etc/kubernetes/controller-manager.config         Sep 11 08:41:26 2031 GMT
/etc/kubernetes/scheduler.config                  Sep 11 08:41:26 2031 GMT
/etc/kubernetes/admin.config                      Sep 11 08:41:26 2031 GMT
/etc/kubernetes/pki/ca.crt                        Sep 11 08:38:53 2031 GMT
/etc/kubernetes/pki/apiserver.crt                 Sep 11 08:41:26 2031 GMT
/etc/kubernetes/pki/apiserver-kubelet-client.crt  Sep 11 08:41:26 2031 GMT
/etc/kubernetes/pki/front-proxy-ca.crt            Sep 11 08:38:54 2031 GMT
/etc/kubernetes/pki/front-proxy-client.crt        Sep 11 08:41:26 2031 GMT
/etc/kubernetes/pki/etcd/ca.crt                   Sep 11 08:38:55 2031 GMT
/etc/kubernetes/pki/etcd/server.crt               Sep 11 08:41:25 2031 GMT
/etc/kubernetes/pki/etcd/peer.crt                 Sep 11 08:41:26 2031 GMT
/etc/kubernetes/pki/etcd/healthcheck-client.crt   Sep 11 08:41:26 2031 GMT
/etc/kubernetes/pki/apiserver-etcd-client.crt     Sep 11 08:41:26 2031 GMT

The following certificates and kubeconfig files will be modified:

/etc/kubernetes
├── admin.conf
├── controller-manager.conf
├── scheduler.conf
├── kubelet.conf
└── pki
    ├── apiserver.crt
    ├── apiserver-etcd-client.crt
    ├── apiserver-kubelet-client.crt
    ├── front-proxy-client.crt
    └── etcd
        ├── healthcheck-client.crt
        ├── peer.crt
        └── server.crt

More info

2. Rollback if failed to renew

The script will back up the /etc/kubernetes directory into /etc/kubernetes.old-$(date +%Y%m%d) (for example: kubernetes.old-20200325)

If the the script is failed to be executed, use the backup directory to overide the /etc/kubernetes directory.

3. Other things

For the clusters of version v1.15.x or higher, there is a command kubeadm alpha certs renew <cert_name> that can renew the certificate. Each time you run this command, the certificate will be extended by 1 year.

Note: For clutsers of version v1.15.x and v1.16.x, there is a bug on kubeadm alpha certs renew <cert_name> command. You need to handle this mannually. See this

This script can handle this so you don't need to worry about that bug.