Configuring a cgroup driver
This page explains how to configure the kubelet cgroup driver to match the container runtime cgroup driver for kubeadm clusters.
Before you begin
You should be familiar with the Kubernetes container runtime requirements.
Configuring the container runtime cgroup driver
The Container runtimes page
explains that the
systemd driver is recommended for kubeadm based setups instead
cgroupfs driver, because kubeadm manages the kubelet as a systemd service.
The page also provides details on how to setup a number of different container runtimes with the
systemd driver by default.
Configuring the kubelet cgroup driver
kubeadm allows you to pass a
KubeletConfiguration structure during
KubeletConfiguration can include the
cgroupDriver field which controls the cgroup
driver of the kubelet.
Kubernetes v1.21 [stable]
If the user is not setting the
kubeadm initwill default it to
A minimal example of configuring the field explicitly:
# kubeadm-config.yaml kind: ClusterConfiguration apiVersion: kubeadm.k8s.io/v1beta2 kubernetesVersion: v1.21 --- kind: KubeletConfiguration apiVersion: kubelet.config.k8s.io/v1beta1 cgroupDriver: systemd
Such a configuration file can then be passed to the kubeadm command:
kubeadm init --config kubeadm-config.yaml
Kubeadm uses the same
KubeletConfigurationfor all nodes in the cluster. The
KubeletConfigurationis stored in a ConfigMap object under the
Executing the sub commands
upgradewould result in kubeadm writing the
KubeletConfigurationas a file under
/var/lib/kubelet/config.yamland passing it to the local node kubelet.
As this guide explains using the
cgroupfs driver with kubeadm is not recommended.
To continue using
cgroupfs and to prevent
kubeadm upgrade from modifying the
KubeletConfiguration cgroup driver on existing setups, you must be explicit
about its value. This applies to a case where you do not wish future versions
of kubeadm to apply the
systemd driver by default.
See the below section on "Modify the kubelet ConfigMap" for details on how to be explicit about the value.
If you wish to configure a container runtime to use the
you must refer to the documentation of the container runtime of your choice.
Migrating to the
To change the cgroup driver of an existing kubeadm cluster to
a similar procedure to a kubelet upgrade is required. This must include both
steps outlined below.
Note: Alternatively, it is possible to replace the old nodes in the cluster with new ones that use the
systemddriver. This requires executing only the first step below before joining the new nodes and ensuring the workloads can safely move to the new nodes before deleting the old nodes.
Modify the kubelet ConfigMap
Find the kubelet ConfigMap name using
kubectl get cm -n kube-system | grep kubelet-config.
kubectl edit cm kubelet-config-x.yy -n kube-system(replace
x.yywith the Kubernetes version).
Either modify the existing
cgroupDrivervalue or add a new field that looks like this:
This field must be present under the
kubelet:section of the ConfigMap.
Update the cgroup driver on all nodes
For each node in the cluster:
- Drain the node using
kubectl drain <node-name> --ignore-daemonsets
- Stop the kubelet using
systemctl stop kubelet
- Stop the container runtime
- Modify the container runtime cgroup driver to
- Start the container runtime
- Start the kubelet using
systemctl start kubelet
- Uncordon the node using
kubectl uncordon <node-name>
Execute these steps on nodes one at a time to ensure workloads have sufficient time to schedule on different nodes.
Once the process is complete ensure that all nodes and workloads are healthy.