Merge pull request #26786 from neolit123/1.21-cgroup-drivers-new-page

kubeadm: add separate page for configuring / migrating cgroup driver

content/en/docs/setup/production-environment/container-runtimes.md

@@ -48,7 +48,7 @@ Changing the settings such that your container runtime and kubelet use `systemd`
 stabilized the system. To configure this for Docker, set `native.cgroupdriver=systemd`.
 
 {{< caution >}}
-Changing the cgroup driver of a Node that has joined a cluster is strongly *not* recommended.  
+Changing the cgroup driver of a Node that has joined a cluster is a sensitive operation.
 If the kubelet has created Pods using the semantics of one cgroup driver, changing the container
 runtime to another cgroup driver can cause errors when trying to re-create the Pod sandbox
 for such existing Pods. Restarting the kubelet may not solve such errors.
@@ -57,6 +57,11 @@ If you have automation that makes it feasible, replace the node with another usi
 configuration, or reinstall it using automation.
 {{< /caution >}}
 
+### Migrating to the `systemd` driver in kubeadm managed clusters
+
+Follow this [Migration guide](/tasks/administer-cluster/kubeadm/configure-cgroup-driver)
+if you wish to migrate to the `systemd` cgroup driver in existing kubeadm managed clusters.
+
 ## Container runtimes
 
 {{% thirdparty-content %}}

content/en/docs/setup/production-environment/tools/kubeadm/install-kubeadm.md

@@ -244,7 +244,7 @@ sudo mkdir -p /opt/cni/bin
 curl -L "https://github.com/containernetworking/plugins/releases/download/${CNI_VERSION}/cni-plugins-linux-amd64-${CNI_VERSION}.tgz" | sudo tar -C /opt/cni/bin -xz
 ```
 
-Define the directory to download command files  
+Define the directory to download command files
 
 {{< note >}}
 The `DOWNLOAD_DIR` variable must be set to a writable directory.
@@ -295,33 +295,17 @@ See the [Kubeadm Troubleshooting guide](/docs/setup/production-environment/tools
 The kubelet is now restarting every few seconds, as it waits in a crashloop for
 kubeadm to tell it what to do.
 
-## Configure cgroup driver used by kubelet on control-plane node
+## Configuring a cgroup driver
 
-When using Docker, kubeadm will automatically detect the cgroup driver for the kubelet
-and set it in the `/var/lib/kubelet/config.yaml` file during runtime.
+Both the container runtime and the kubelet have a property called
+["cgroup driver"](/docs/setup/production-environment/container-runtimes/), which is important
+for the management of cgroups on Linux machines.
 
-If you are using a different CRI, you must pass your `cgroupDriver` value to `kubeadm init`, like so:
-
-```yaml
-apiVersion: kubelet.config.k8s.io/v1beta1
-kind: KubeletConfiguration
-cgroupDriver: <value>
-```
-
-For further details, please read [Using kubeadm init with a configuration file](/docs/reference/setup-tools/kubeadm/kubeadm-init/#config-file).
-
-Please mind, that you **only** have to do that if the cgroup driver of your CRI
-is not `cgroupfs`, because that is the default value in the kubelet already.
-
-{{< note >}}
-Since `--cgroup-driver` flag has been deprecated by the kubelet, if you have that in `/var/lib/kubelet/kubeadm-flags.env`
-or `/etc/default/kubelet`(`/etc/sysconfig/kubelet` for RPMs), please remove it and use the KubeletConfiguration instead
-(stored in `/var/lib/kubelet/config.yaml` by default).
-{{< /note >}}
-
-The automatic detection of cgroup driver for other container runtimes
-like CRI-O and containerd is work in progress.
+{{< warning >}}
+Matching the container runtime and kubelet cgroup drivers is required or otherwise the kubelet process will fail.
+{{< warning >}}
 
+See [Configuring a cgroup driver](/tasks/administer-cluster/kubeadm/configure-cgroup-driver) for more details.
 
 ## Troubleshooting