Introduction

Kucero (KUbernetes CErtificate ROtation) is a Kubernetes daemonset that performs automatic Kubernetes control plane certificate rotation.

Kucero takes care both:

• kubeadm certificates and kubeconfigs: kucero periodically watches the kubeadm generated certificates and kubeconfigs on host system, and renews certificates/kubeconfigs when the certificates/kubeconfigs residual time is below than user configured time period.
• kubelet certificates:
  • kubelet.conf: kucero helps on auto-update the /etc/kubernetes/kubelet.conf from embedded base64 encoded client cert/key to using the local file /var/lib/kubelet/kubelet-client-current.pem (this is a bug if you bootstrap a cluster with kubeadm version < 1.17).
  • client certificate: kucero helps on configuring rotateCertificates: true or rotateCertificates: false in /var/lib/kubelet/config.yaml which controls to auto rotates the kubelet client certificate or not. When configures rotateCertificates: true, the kubelet sends out the client CSR at approximately 70%-90% of the total lifetime of the certificate, then the kube-controler-manager watches kubelet client CSR, and then auto signs and approves kubelet client certificates with Kubernetes cluster CA cert/key pair.
  • server certificate: kucero helps on configuring serverTLSBootstrap: true or serverTLSBootstrap: false in /var/lib/kubelet/config.yaml which controls to auto rotates the kubelet server certificate or not. When configures serverTLSBootstrap: true, the kubelet sends out the server CSR at approximately 70%-90% of the total lifetime of the certificate, then the kucero controller watches kubelet server CSR, and then auto signs and approves kubelet server certificates with user-specified CA cert/key pair.

Kubelet Configuration

By default, kucero enables kubelet client rotateCertificates: true and server certificates serverTLSBootstrap: true auto rotation, you could disable it by passing flags to kucero:

• --enable-kubelet-client-cert-rotation=false
• --enable-kubelet-server-cert-rotation=false

Build Requirements

• Golang >= 1.21
• Docker
• Kustomize

Kubeadm Compatibility

• kubeadm >= 1.15.0

Installation

make docker-build IMG=<YOUR-DOCKER-REPOSITORY-IMAGE-NAME-TAG>
make docker-push IMG=<YOUR-DOCKER-REPOSITORY-IMAGE-NAME-TAG>
make deploy-manifest IMG=<YOUR-DOCKER-REPOSITORY-IMAGE-NAME-TAG>

Configuration

The following arguments can be passed to kucero via the daemonset pod template:

Flags:
      --ca-cert-path string         sign CSR with this certificate file (default "/etc/kubernetes/pki/ca.crt")
      --ca-key-path string          sign CSR with this private key file (default "/etc/kubernetes/pki/ca.key")
      --ds-name string              name of daemonset on which to place lock (default "kucero")
      --ds-namespace string         namespace containing daemonset on which to place lock (default "kube-system")
      --enable-kucero-controller    enable kucero controller (default true)
  -h, --help                        help for kucero
      --leader-election-id string   the name of the configmap used to coordinate leader election between kucero-controllers (default "kucero-leader-election")
      --lock-annotation string      annotation in which to record locking node (default "caasp.suse.com/kucero-node-lock")
      --metrics-addr string         the address the metric endpoint binds to (default ":8080")
      --polling-period duration     certificate rotation check period (default 1h0m0s)
      --renew-before duration       rotates certificate before expiry is below (default 720h0m0s)

Uninstallation

make destroy-manifest

Demo

• kubeadm
• kubelet