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add note for cgroup v1 deprecation during kubelet upgrade #53082

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add note for cgroup v1 deprecation during kubelet upgrade #53082

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10 changes: 10 additions & 0 deletions content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade.md
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Expand Up @@ -241,6 +241,16 @@ kubectl drain <node-to-drain> --ignore-daemonsets

### Upgrade kubelet and kubectl

{{< note >}}
FailCgroupV1 is a kubelet configuration option that is set to 'true' by default.
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@lmktfy lmktfy Nov 4, 2025

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Style and wording nit:

Suggested change
FailCgroupV1 is a kubelet configuration option that is set to 'true' by default.
On Linux nodes, the kubelet defaults to supporting only cgroups v2.
For Kubernetes {{< skew currentVersion >}} the `FailCgroupV1` kubelet configuration option is set to true by default.

If you are using cgroups v1, kubelet will fail to start if the FailCgroupV1 is not set.
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@lmktfy lmktfy Nov 4, 2025

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Suggested change
If you are using cgroups v1, kubelet will fail to start if the FailCgroupV1 is not set.
If you are using cgroups v1 and the `FailCgroupV1` setting is not set to true,
the kubelet reports an error and fails to start.

The cgroups v1 support is deprecated and will be removed in a future release.
If you are using cgroups v1, you should migrate to cgroups v2.
To explicitly enable cgroups v1 support for kubelet v1.35 or newer,
you must set the kubelet configuration option 'FailCgroupV1' to 'false'. You must also explicitly skip this validation.
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@lmktfy lmktfy Nov 4, 2025

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Suggested change
you must set the kubelet configuration option 'FailCgroupV1' to 'false'. You must also explicitly skip this validation.
you **must** set the kubelet configuration option `FailCgroupV1` to false. You must also explicitly skip this kubeadm validation.

For more information, see https://git.k8s.io/enhancements/keps/sig-node/5573-remove-cgroup-v1.
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@lmktfy lmktfy Nov 4, 2025

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We should link to the docs about the deprecation, not to the KEP.

{{</ note >}}

1. Upgrade the kubelet and kubectl:

{{< tabs name="k8s_install_kubelet" >}}
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10 changes: 10 additions & 0 deletions content/en/docs/tasks/administer-cluster/kubeadm/upgrading-linux-nodes.md
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Expand Up @@ -75,6 +75,16 @@ kubectl drain <node-to-drain> --ignore-daemonsets

### Upgrade kubelet and kubectl

{{< note >}}
FailCgroupV1 is a kubelet configuration option that is set to 'true' by default since v1.35.
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@lmktfy lmktfy Nov 4, 2025

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Style and wording nit:

Suggested change
FailCgroupV1 is a kubelet configuration option that is set to 'true' by default since v1.35.
On Linux nodes, the kubelet defaults to supporting only cgroups v2.
For Kubernetes {{< skew currentVersion >}} the `FailCgroupV1` kubelet configuration option is set to true by default.

If you are using cgroups v1, kubelet will fail to start if the FailCgroupV1 is not set..
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@lmktfy lmktfy Nov 4, 2025

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Suggested change
If you are using cgroups v1, kubelet will fail to start if the FailCgroupV1 is not set..
If you are using cgroups v1 and the `FailCgroupV1` setting is not set to true,
the kubelet reports an error and fails to start.

The cgroups v1 support is deprecated and will be removed in a future release.
If you are using cgroups v1, you should migrate to cgroups v2.
To explicitly enable cgroups v1 support for kubelet v1.35 or newer,
you must set the kubelet configuration option 'FailCgroupV1' to 'false'. You must also explicitly skip this validation.
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@lmktfy lmktfy Nov 4, 2025

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Suggested change
you must set the kubelet configuration option 'FailCgroupV1' to 'false'. You must also explicitly skip this validation.
you **must** set the kubelet configuration option `FailCgroupV1` to false. You must also explicitly skip this kubeadm validation.

For more information, see https://git.k8s.io/enhancements/keps/sig-node/5573-remove-cgroup-v1.
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@lmktfy lmktfy Nov 4, 2025

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We should link to the docs about the deprecation, not to the KEP.

{{</ note >}}

1. Upgrade the kubelet and kubectl:

{{< tabs name="k8s_kubelet_and_kubectl" >}}
Expand Down