<p>We currently having 2 Master 2 Worker node cluster on <strong>Kubernetes v1.13.4</strong>.The cluster is down as the kubelet certificate located in <code>/var/lib/kubelet/pki/kubelet.crt</code> has expired and the kubelet service is not running. On checking the kubelet logs I get the following error</p>

<blockquote>
  <p>E0808 09:49:35.126533   55154 bootstrap.go:209] Part of the existing bootstrap client certificate is expired: 2019-08-06 22:39:23 +0000 UTC</p>
</blockquote>

<p>The following certificates <code>ca.crt</code>, <code>apiserver-kubelet-client.crt</code> are valid. We are unable to renew the <code>kubelet.crt</code> certificate manually by using the <strong>kubeadm-config.yaml</strong>. Can someone please provide the steps to renew the certificate.</p>

<p>We have tried setting  <code>--rotate-certificates</code> property and also using <strong>kubeadm-config.yaml</strong> but since we are using <strong>v1.13.4</strong> <code>kubeadm --config</code> flag is <strong>not present</strong>.</p>

<p>On checking the kubelet logs I get the following error</p>

<blockquote>
  <p>E0808 09:49:35.126533   55154 bootstrap.go:209] Part of the existing bootstrap client certificate is expired: 2019-08-06 22:39:23 +0000 UTC</p>
</blockquote>

<p>As you mentioned that only <code>kubelet.crt</code> has expired and <code>apiserver-kubelet-client.crt</code> is valid, you can try to renew it by command <code>kubeadm alpha certs renew</code> based on <a href="https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-certs/#manual-certificate-renewal" rel="nofollow noreferrer">documentation</a>.</p>

<p>Second way to renew kubeadm certificates is upgrade version like in <a href="https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade-1-14/" rel="nofollow noreferrer">this article</a>.</p>

<p>You can also try by using <code>kubeadm init phase certs all</code>. It was explained in <a href="https://stackoverflow.com/questions/56320930/renew-kubernetes-pki-after-expired">this Stackoverflow</a> case.</p>

<p>Let me know if that helped. If not provide more information with more logs.</p>
