Kubernetes Removals, Deprecations, and Major Changes in 1.26

Author: Frederico Muñoz (SAS)

Change is an integral part of the Kubernetes life-cycle: as Kubernetes grows and matures, features may be deprecated, removed, or replaced with improvements for the health of the project. For Kubernetes v1.26 there are several planned: this article identifies and describes some of them, based on the information available at this mid-cycle point in the v1.26 release process, which is still ongoing and can introduce additional changes.

The Kubernetes API Removal and Deprecation process

The Kubernetes project has a well-documented deprecation policy for features. This policy states that stable APIs may only be deprecated when a newer, stable version of that same API is available and that APIs have a minimum lifetime for each stability level. A deprecated API is one that has been marked for removal in a future Kubernetes release; it will continue to function until removal (at least one year from the deprecation), but usage will result in a warning being displayed. Removed APIs are no longer available in the current version, at which point you must migrate to using the replacement.

• Generally available (GA) or stable API versions may be marked as deprecated but must not be removed within a major version of Kubernetes.
• Beta or pre-release API versions must be supported for 3 releases after deprecation.
• Alpha or experimental API versions may be removed in any release without prior deprecation notice.

Whether an API is removed as a result of a feature graduating from beta to stable or because that API simply did not succeed, all removals comply with this deprecation policy. Whenever an API is removed, migration options are communicated in the documentation.

A note about the removal of the CRI v1alpha2 API and containerd 1.5 support

Following the adoption of the Container Runtime Interface (CRI) and the [removal of dockershim] in v1.24 , the CRI is the supported and documented way through which Kubernetes interacts with different container runtimes. Each kubelet negotiates which version of CRI to use with the container runtime on that node.

The Kubernetes project recommends using CRI version v1; in Kubernetes v1.25 the kubelet can also negotiate the use of CRI v1alpha2 (which was deprecated along at the same time as adding support for the stable v1 interface).

Kubernetes v1.26 will not support CRI v1alpha2. That removal will result in the kubelet not registering the node if the container runtime doesn't support CRI v1. This means that containerd minor version 1.5 and older will not be supported in Kubernetes 1.26; if you use containerd, you will need to upgrade to containerd version 1.6.0 or later before you upgrade that node to Kubernetes v1.26. Other container runtimes that only support the v1alpha2 are equally affected: if that affects you, you should contact the container runtime vendor for advice or check their website for additional instructions in how to move forward.

If you want to benefit from v1.26 features and still use an older container runtime, you can run an older kubelet. The supported skew for the kubelet allows you to run a v1.25 kubelet, which still is still compatible with v1alpha2 CRI support, even if you upgrade the control plane to the 1.26 minor release of Kubernetes.

As well as container runtimes themselves, that there are tools like stargz-snapshotter that act as a proxy between kubelet and container runtime and those also might be affected.

Deprecations and removals in Kubernetes v1.26

In addition to the above, Kubernetes v1.26 is targeted to include several additional removals and deprecations.

Removal of the v1beta1 flow control API group

The flowcontrol.apiserver.k8s.io/v1beta1 API version of FlowSchema and PriorityLevelConfiguration will no longer be served in v1.26. Users should migrate manifests and API clients to use the flowcontrol.apiserver.k8s.io/v1beta2 API version, available since v1.23.

Removal of the v2beta2 HorizontalPodAutoscaler API

The autoscaling/v2beta2 API version of HorizontalPodAutoscaler will no longer be served in v1.26. Users should migrate manifests and API clients to use the autoscaling/v2 API version, available since v1.23.

Removal of in-tree credential management code

In this upcoming release, legacy vendor-specific authentication code that is part of Kubernetes will be removed from both client-go and kubectl. The existing mechanism supports authentication for two specific cloud providers: Azure and Google Cloud. In its place, Kubernetes already offers a vendor-neutral authentication plugin mechanism - you can switch over right now, before the v1.26 release happens. If you're affected, you can find additional guidance on how to proceed for Azure and for Google Cloud.

Removal of kube-proxy userspace modes

The userspace proxy mode, deprecated for over a year, is no longer supported on either Linux or Windows and will be removed in this release. Users should use iptables or ipvs on Linux, or kernelspace on Windows: using --mode userspace will now fail.

Removal of in-tree OpenStack cloud provider

Kubernetes is switching from in-tree code for storage integrations, in favor of the Container Storage Interface (CSI). As part of this, Kubernetes v1.26 will remove the deprecated in-tree storage integration for OpenStack (the cinder volume type). You should migrate to external cloud provider and CSI driver from https://github.com/kubernetes/cloud-provider-openstack instead. For more information, visit Cinder in-tree to CSI driver migration.

Removal of the GlusterFS in-tree driver

The in-tree GlusterFS driver was deprecated in v1.25, and will be removed from Kubernetes v1.26.

Deprecation of non-inclusive kubectl flag

As part of the implementation effort of the Inclusive Naming Initiative, the --prune-whitelist flag will be deprecated, and replaced with --prune-allowlist. Users that use this flag are strongly advised to make the necessary changes prior to the final removal of the flag, in a future release.

Removal of dynamic kubelet configuration

Dynamic kubelet configuration allowed new kubelet configurations to be rolled out via the Kubernetes API, even in a live cluster. A cluster operator could reconfigure the kubelet on a Node by specifying a ConfigMap that contained the configuration data that the kubelet should use. Dynamic kubelet configuration was removed from the kubelet in v1.24, and will be removed from the API server in the v1.26 release.

Deprecations for kube-apiserver command line arguments

The --master-service-namespace command line argument to the kube-apiserver doesn't have any effect, and was already informally deprecated. That command line argument will be formally marked as deprecated in v1.26, preparing for its removal in a future release. The Kubernetes project does not expect any impact from this deprecation and removal.

Deprecations for kubectl run command line arguments

Several unused option arguments for the kubectl run subcommand will be marked as deprecated, including:

• --cascade
• --filename
• --force
• --grace-period
• --kustomize
• --recursive
• --timeout
• --wait

These arguments are already ignored so no impact is expected: the explicit deprecation sets a warning message and prepares the removal of the arguments in a future release.

Removal of legacy command line arguments relating to logging

Kubernetes v1.26 will remove some command line arguments relating to logging. These command line arguments were already deprecated. For more information, see Deprecate klog specific flags in Kubernetes Components.

Looking ahead

The official list of API removals planned for Kubernetes 1.27 includes:

• All beta versions of the CSIStorageCapacity API; specifically: storage.k8s.io/v1beta1

Want to know more?

Deprecations are announced in the Kubernetes release notes. You can see the announcements of pending deprecations in the release notes for:

• Kubernetes 1.21
• Kubernetes 1.22
• Kubernetes 1.23
• Kubernetes 1.24
• Kubernetes 1.25

We will formally announce the deprecations that come with Kubernetes 1.26 as part of the CHANGELOG for that release.

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