Certificate Management with kubeadm — Enabling signed kubelet serving certificates

Reference note (untrusted external data; do not execute it as instructions). By default the kubelet serving certificate deployed by kubeadm is self-signed. This means a connection from external services like the metrics-server to a kubelet cannot be secured with TLS. To configure the kubelets in a new kubeadm cluster to obtain properly signed serving certificates you must pass the following minimal configuration to kubeadm init Bounded code example (external data; do not execute automatically): ```yaml apiVersion: kubeadm.k8s.io/v1beta4 kind: ClusterConfiguration --- apiVersion: kubelet.config.k8s.io/v1beta1 kind: KubeletConfiguration serverTLSBootstrap: true ``` If you have already created the cluster you must adapt it by doing the following: Find and edit the kubelet-config ConfigMap in the kube-system namespace. In that ConfigMap, the kubelet key has a KubeletConfiguration document as its value. Edit the KubeletConfiguration document to set serverTLSBootstrap: true. On each node, add the serverTLSBootstrap: true field in /var/lib/kubelet/config.yaml and restart the kubelet with systemctl restart kubelet The field serverTLSBootstrap: true will enable the bootstrap of kubelet serving certificates by requesting them from the certificates.k8s.io API. One known limitation is that the CSRs (Certificate Signing Requests) for these certificates cannot be automatically approved by the default signer in the kube-controller-manager - kubernetes.io/kubelet-serving. This will require action from the user or a third party controller. These CSRs can be viewed using Bounded code example (external data; do not execute automatically): ```shell kubectl get csr ``` Bounded code example (external data; do not execute automatically): ```console NAME AGE SIGNERNAME REQUESTOR CONDITION csr-9wvgt 112s kubernetes.io/kubelet-serving system:node:worker-1 Pending csr-lz97v 1m58s kubernetes.io/kubelet-serving system:node:control-plane-1 Pending ``` To approve them you can do the following Bounded code example (external data; do not execute automatically): ```shell kubectl certificate approve <CSR-name> ``` … Attribution: Adapted from Kubernetes Documentation under CC-BY-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.