<p>My certificates were expired:</p>
<pre><code>root@ubuntu:~# kubectl get pods
Unable to connect to the server: x509: certificate has expired or is not yet valid                                                                                                                                                           
</code></pre>
<p>I verified it by running:</p>
<pre><code>root@ubuntu:~# 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'
[check-expiration] Error reading configuration from the Cluster. Falling back to default configuration

W0330 09:18:49.875780   12562 configset.go:202] WARNING: kubeadm cannot validate component configs for API groups [kubelet.config.k8s.io kubepro                                                                                             xy.config.k8s.io]
CERTIFICATE                EXPIRES                  RESIDUAL TIME   CERTIFICATE AUTHORITY   EXTERNALLY MANAGED
admin.conf                 Mar 29, 2021 09:27 UTC   &lt;invalid&gt;                               no
apiserver                  Mar 29, 2021 09:27 UTC   &lt;invalid&gt;       ca                      no
apiserver-etcd-client      Mar 29, 2021 09:27 UTC   &lt;invalid&gt;       etcd-ca                 no
apiserver-kubelet-client   Mar 29, 2021 09:27 UTC   &lt;invalid&gt;       ca                      no
controller-manager.conf    Mar 29, 2021 09:27 UTC   &lt;invalid&gt;                               no
etcd-healthcheck-client    Mar 29, 2021 09:27 UTC   &lt;invalid&gt;       etcd-ca                 no
etcd-peer                  Mar 29, 2021 09:27 UTC   &lt;invalid&gt;       etcd-ca                 no
etcd-server                Mar 29, 2021 09:27 UTC   &lt;invalid&gt;       etcd-ca                 no
front-proxy-client         Mar 29, 2021 09:27 UTC   &lt;invalid&gt;       front-proxy-ca          no
scheduler.conf             Mar 29, 2021 09:27 UTC   &lt;invalid&gt;                               no

CERTIFICATE AUTHORITY   EXPIRES                  RESIDUAL TIME   EXTERNALLY MANAGED
ca                      Mar 27, 2030 09:27 UTC   8y              no
etcd-ca                 Mar 27, 2030 09:27 UTC   8y              no
front-proxy-ca          Mar 27, 2030 09:27 UTC   8y              no
</code></pre>
<p>I renew the certificates by running: <code>kubeadm alpha certs renew all</code>.</p>
<pre><code>W0330 09:20:21.951839   13124 configset.go:202] WARNING: kubeadm cannot validate component configs for API groups [kubelet.config.k8s.io kubeproxy.config.k8s.io]
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
</code></pre>
<p>All the certificates are now updated to 2022 so it should be okay:</p>
<pre><code>CERTIFICATE                EXPIRES                  RESIDUAL TIME   CERTIFICATE AUTHORITY   EXTERNALLY MANAGED
admin.conf                 Mar 30, 2022 09:20 UTC   364d                                    no
apiserver                  Mar 30, 2022 09:20 UTC   364d            ca                      no
apiserver-etcd-client      Mar 30, 2022 09:20 UTC   364d            etcd-ca                 no
apiserver-kubelet-client   Mar 30, 2022 09:20 UTC   364d            ca                      no
controller-manager.conf    Mar 30, 2022 09:20 UTC   364d                                    no
etcd-healthcheck-client    Mar 30, 2022 09:20 UTC   364d            etcd-ca                 no
etcd-peer                  Mar 30, 2022 09:20 UTC   364d            etcd-ca                 no
etcd-server                Mar 30, 2022 09:20 UTC   364d            etcd-ca                 no
front-proxy-client         Mar 30, 2022 09:20 UTC   364d            front-proxy-ca          no
scheduler.conf             Mar 30, 2022 09:20 UTC   364d                                    no

CERTIFICATE AUTHORITY   EXPIRES                  RESIDUAL TIME   EXTERNALLY MANAGED
ca                      Mar 27, 2030 09:27 UTC   8y              no
etcd-ca                 Mar 27, 2030 09:27 UTC   8y              no
front-proxy-ca          Mar 27, 2030 09:27 UTC   8y              no
</code></pre>
<p>But when I run <code>kubectl get pods</code> I received the error:</p>
<pre><code>error: You must be logged in to the server (Unauthorized)
</code></pre>
<p>It should be a problem with the certificate I think, but I am not sure how to fix it. Should I create new certificate and replace the one that inside the config file?</p>

<p>The <code>~/.kube/config</code> wasn't updated with the changes.</p>
<p>I ran:</p>
<pre><code>mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config  
</code></pre>
<p>and it fixed it.</p>
