Kubernetes API and Feature Removals In 1.22: Here’s What You Need To Know

Authors: Krishna Kilari (Amazon Web Services), Tim Bannister (The Scale Factory)

As the Kubernetes API evolves, APIs are periodically reorganized or upgraded. When APIs evolve, the old APIs they replace are deprecated, and eventually removed. See Kubernetes API removals to read more about Kubernetes' policy on removing APIs.

We want to make sure you're aware of some upcoming removals. These are beta APIs that you can use in current, supported Kubernetes versions, and they are already deprecated. The reason for all of these removals is that they have been superseded by a newer, stable (“GA”) API.

Kubernetes 1.22, due for release in August 2021, will remove a number of deprecated APIs. Update: Kubernetes 1.22: Reaching New Peaks has details on the v1.22 release.

API removals for Kubernetes v1.22

The v1.22 release will stop serving the API versions we've listed immediately below. These are all beta APIs that were previously deprecated in favor of newer and more stable API versions.

• Beta versions of the ValidatingWebhookConfiguration and MutatingWebhookConfiguration API (the admissionregistration.k8s.io/v1beta1 API versions)
• The beta CustomResourceDefinition API (apiextensions.k8s.io/v1beta1)
• The beta APIService API (apiregistration.k8s.io/v1beta1)
• The beta TokenReview API (authentication.k8s.io/v1beta1)
• Beta API versions of SubjectAccessReview, LocalSubjectAccessReview, SelfSubjectAccessReview (API versions from authorization.k8s.io/v1beta1)
• The beta CertificateSigningRequest API (certificates.k8s.io/v1beta1)
• The beta Lease API (coordination.k8s.io/v1beta1)
• All beta Ingress APIs (the extensions/v1beta1 and networking.k8s.io/v1beta1 API versions)

The Kubernetes documentation covers these API removals for v1.22 and explains how each of those APIs change between beta and stable.

What to do

We're going to run through each of the resources that are affected by these removals and explain the steps you'll need to take.

Ingress

Migrate to use the networking.k8s.io/v1 Ingress API, available since v1.19.
The related API IngressClass is designed to complement the Ingress concept, allowing you to configure multiple kinds of Ingress within one cluster. If you're currently using the deprecated kubernetes.io/ingress.class annotation, plan to switch to using the .spec.ingressClassName field instead.
On any cluster running Kubernetes v1.19 or later, you can use the v1 API to retrieve or update existing Ingress objects, even if they were created using an older API version.

When you convert an Ingress to the v1 API, you should review each rule in that Ingress. Older Ingresses use the legacy ImplementationSpecific path type. Instead of ImplementationSpecific, switch path matching to either Prefix or Exact. One of the benefits of moving to these alternative path types is that it becomes easier to migrate between different Ingress classes.

ⓘ As well as upgrading your own use of the Ingress API as a client, make sure that every ingress controller that you use is compatible with the v1 Ingress API. Read Ingress Prerequisites for more context about Ingress and ingress controllers.

ValidatingWebhookConfiguration and MutatingWebhookConfiguration

Migrate to use the admissionregistration.k8s.io/v1 API versions of ValidatingWebhookConfiguration and MutatingWebhookConfiguration, available since v1.16.
You can use the v1 API to retrieve or update existing objects, even if they were created using an older API version.

CustomResourceDefinition

Migrate to use the CustomResourceDefinition apiextensions.k8s.io/v1 API, available since v1.16.
You can use the v1 API to retrieve or update existing objects, even if they were created using an older API version. If you defined any custom resources in your cluster, those are still served after you upgrade.

If you're using external CustomResourceDefinitions, you can use kubectl convert to translate existing manifests to use the newer API. Because there are some functional differences between beta and stable CustomResourceDefinitions, our advice is to test out each one to make sure it works how you expect after the upgrade.

APIService

Migrate to use the apiregistration.k8s.io/v1 APIService API, available since v1.10.
You can use the v1 API to retrieve or update existing objects, even if they were created using an older API version. If you already have API aggregation using an APIService object, this aggregation continues to work after you upgrade.

TokenReview

Migrate to use the authentication.k8s.io/v1 TokenReview API, available since v1.10.

As well as serving this API via HTTP, the Kubernetes API server uses the same format to send TokenReviews to webhooks. The v1.22 release continues to use the v1beta1 API for TokenReviews sent to webhooks by default. See Looking ahead for some specific tips about switching to the stable API.

SubjectAccessReview, SelfSubjectAccessReview and LocalSubjectAccessReview

Migrate to use the authorization.k8s.io/v1 versions of those authorization APIs, available since v1.6.

CertificateSigningRequest

Migrate to use the certificates.k8s.io/v1 CertificateSigningRequest API, available since v1.19.
You can use the v1 API to retrieve or update existing objects, even if they were created using an older API version. Existing issued certificates retain their validity when you upgrade.

Lease

Migrate to use the coordination.k8s.io/v1 Lease API, available since v1.14.
You can use the v1 API to retrieve or update existing objects, even if they were created using an older API version.

kubectl convert

There is a plugin to kubectl that provides the kubectl convert subcommand. It's an official plugin that you can download as part of Kubernetes. See Download Kubernetes for more details.

You can use kubectl convert to update manifest files to use a different API version. For example, if you have a manifest in source control that uses the beta Ingress API, you can check that definition out, and run kubectl convert -f <manifest> --output-version <group>/<version>. You can use the kubectl convert command to automatically convert an existing manifest.

For example, to convert an older Ingress definition to networking.k8s.io/v1, you can run:

kubectl convert -f ./legacy-ingress.yaml --output-version networking.k8s.io/v1

The automatic conversion uses a similar technique to how the Kubernetes control plane updates objects that were originally created using an older API version. Because it's a mechanical conversion, you might need to go in and change the manifest to adjust defaults etc.

Rehearse for the upgrade

If you manage your cluster's API server component, you can try out these API removals before you upgrade to Kubernetes v1.22.

To do that, add the following to the kube-apiserver command line arguments:

--runtime-config=admissionregistration.k8s.io/v1beta1=false,apiextensions.k8s.io/v1beta1=false,apiregistration.k8s.io/v1beta1=false,authentication.k8s.io/v1beta1=false,authorization.k8s.io/v1beta1=false,certificates.k8s.io/v1beta1=false,coordination.k8s.io/v1beta1=false,extensions/v1beta1/ingresses=false,networking.k8s.io/v1beta1=false

(as a side effect, this also turns off v1beta1 of EndpointSlice - watch out for that when you're testing).

Once you've switched all the kube-apiservers in your cluster to use that setting, those beta APIs are removed. You can test that API clients (kubectl, deployment tools, custom controllers etc) still work how you expect, and you can revert if you need to without having to plan a more disruptive downgrade.

Advice for software authors

Maybe you're reading this because you're a developer of an addon or other component that integrates with Kubernetes?

If you develop an Ingress controller, webhook authenticator, an API aggregation, or any other tool that relies on these deprecated APIs, you should already have started to switch your software over.

You can use the tips in Rehearse for the upgrade to run your own Kubernetes cluster that only uses the new APIs, and make sure that your code works OK. For your documentation, make sure readers are aware of any steps they should take for the Kubernetes v1.22 upgrade.

Where possible, give your users a hand to adopt the new APIs early - perhaps in a test environment - so they can give you feedback about any problems.

There are some more deprecations coming in Kubernetes v1.25, so plan to have those covered too.

Kubernetes API removals

Here's some background about why Kubernetes removes some APIs, and also a promise about stable APIs in Kubernetes.

Kubernetes follows a defined deprecation policy for its features, including the Kubernetes API. That policy allows for replacing stable (“GA”) APIs from Kubernetes. Importantly, this policy means that a stable API only be deprecated when a newer stable version of that same API is available.

That stability guarantee matters: if you're using a stable Kubernetes API, there won't ever be a new version released that forces you to switch to an alpha or beta feature.

Earlier stages are different. Alpha features are under test and potentially incomplete. Almost always, alpha features are disabled by default. Kubernetes releases can and do remove alpha features that haven't worked out.

After alpha, comes beta. These features are typically enabled by default; if the testing works out, the feature can graduate to stable. If not, it might need a redesign.

Last year, Kubernetes officially adopted a policy for APIs that have reached their beta phase:

For Kubernetes REST APIs, when a new feature's API reaches beta, that starts a countdown. The beta-quality API now has three releases … to either:

• reach GA, and deprecate the beta, or
• have a new beta version (and deprecate the previous beta).

At the time of that article, three Kubernetes releases equated to roughly nine calendar months. Later that same month, Kubernetes adopted a new release cadence of three releases per calendar year, so the countdown period is now roughly twelve calendar months.

Whether an API removal is because of a beta feature graduating to stable, or because that API hasn't proved successful, Kubernetes will continue to remove APIs by following its deprecation policy and making sure that migration options are documented.

Looking ahead

There's a setting that's relevant if you use webhook authentication checks. A future Kubernetes release will switch to sending TokenReview objects to webhooks using the authentication.k8s.io/v1 API by default. At the moment, the default is to send authentication.k8s.io/v1beta1 TokenReviews to webhooks, and that's still the default for Kubernetes v1.22. However, you can switch over to the stable API right now if you want: add --authentication-token-webhook-version=v1 to the command line options for the kube-apiserver, and check that webhooks for authentication still work how you expected.

Once you're happy it works OK, you can leave the --authentication-token-webhook-version=v1 option set across your control plane.

The v1.25 release that's planned for next year will stop serving beta versions of several Kubernetes APIs that are stable right now and have been for some time. The same v1.25 release will remove PodSecurityPolicy, which is deprecated and won't graduate to stable. See PodSecurityPolicy Deprecation: Past, Present, and Future for more information.

The official list of API removals planned for Kubernetes 1.25 is:

• The beta CronJob API (batch/v1beta1)
• The beta EndpointSlice API (networking.k8s.io/v1beta1)
• The beta PodDisruptionBudget API (policy/v1beta1)
• The beta PodSecurityPolicy API (policy/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 1.19, 1.20, and 1.21.

For information on the process of deprecation and removal, check out the official Kubernetes deprecation policy document.

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