Deprecated Kubernetes APIs

Kubernetes is an API-driven system and the API evolves over time to reflect the evolving understanding of the problem space. This is common practice across systems and their APIs. An important part of evolving APIs is a good deprecation policy and process to inform users of how changes to APIs are implemented. In other words, consumers of your API need to know in advance and in what release an API will be removed or changed. This removes the element of surprise and breaking changes to consumers.

The Kubernetes deprecation policy documents how Kubernetes handles the changes to its API versions. The policy for deprecation states the timeframe that API versions will be supported following a deprecation announcement. It is therefore important to be aware of deprecation announcements and know when API versions will be removed, to help minimize the effect.

This is an example of an announcement for the removal of deprecated API versions in Kubernetes 1.16 and was advertised a few months prior to the release. These API versions would have been announced for deprecation prior to this again. This shows that there is a good policy in place which informs consumers of API version support.

Helm templates specify a Kubernetes API group when defining a Kubernetes object, similar to a Kubernetes manifest file. It is specified in the apiVersion field of the template and it identifies the API version of the Kubernetes object. This means that Helm users and chart maintainers need to be aware when Kubernetes API versions have been deprecated and in what Kubernetes version they will be removed.

Chart Maintainers

You should audit your charts checking for Kubernetes API versions that are deprecated or are removed in a Kubernetes version. The API versions found as due to be or that are now out of support, should be updated to the supported version and a new version of the chart released. The API version is defined by the kind and apiVersion fields. For example, here is a removed Deployment object API version in Kubernetes 1.16:

apiVersion: apps/v1beta1
kind: Deployment

Helm Users

You should audit the charts that you use (similar to chart maintainers) and identify any charts where API versions are deprecated or removed in a Kubernetes version. For the charts identified, you need to check for the latest version of the chart (which has supported API versions) or update the chart yourself.

Additionally, you also need to audit any charts deployed (i.e. Helm releases) checking again for any deprecated or removed API versions. This can be done by getting details of a release using the helm get manifest command.

The means for updating a Helm release to supported APIs depends on your findings as follows:

  1. If you find deprecated API versions only then:
  • Perform a helm upgrade with a version of the chart with supported Kubernetes API versions
  • Add a description in the upgrade, something along the lines to not perform a rollback to a Helm version prior to this current version
  1. If you find any API version(s) that is/are removed in a Kubernetes version then:
  • If you are running a Kubernetes version where the API version(s) are still available (for example, you are on Kubernetes 1.15 and found you use APIs that will be removed in Kubernetes 1.16):
    • Follow the step 1 procedure
  • Otherwise (for example, you are already running a Kubernetes version where some API versions reported by helm get manifest are no longer available):

Note: In all cases of updating a Helm release with supported APIs, you should never rollback the release to a version prior to the release version with the supported APIs.

Recommendation: The best practice is to upgrade releases using deprecated API versions to supported API versions, prior to upgrading to a kubernetes cluster that removes those API versions.

If you don't update a release as suggested previously, you will have an error similar to the following when trying to upgrade a release in a Kubernetes version where its API version(s) is/are removed:

Error: UPGRADE FAILED: current release manifest contains removed kubernetes api(s)
for this kubernetes version and it is therefore unable to build the kubernetes
objects for performing the diff. error from kubernetes: unable to recognize "":
no matches for kind "Deployment" in version "apps/v1beta1"

Helm fails in this scenario because it attempts to create a diff patch between the current deployed release (which contains the Kubernetes APIs that are removed in this Kubernetes version) against the chart you are passing with the updated/supported API versions. The underlying reason for failure is that when Kubernetes removes an API version, the Kubernetes Go client library can no longer parse the deprecated objects and Helm therefore fails when calling the library. Helm unfortunately is unable to recover from this situation and is no longer able to manage such a release. See Updating API Versions of a Release Manifest for more details on how to recover from this scenario.

Updating API Versions of a Release Manifest

The manifest is a property of the Helm release object which is stored in the data field of a Secret (default) or ConfigMap in the cluster. The data field contains a gzipped object which is base 64 encoded twice. There is a Secret/ConfigMap per release version/revision in the namespace of the release.

You can use the Helm mapkubeapis plugin to perform the update of a release to supported APIs. Check out the readme for more details.

Alternatively, you can follow these manual steps to perform an update of the API versions of a release manifest:

  • Get the name of the latest deployed release: kubectl get secret -l owner=helm,status=deployed,name=<release_name> --namespace <release_namespace> | awk '{print $1}' | grep -v NAME
  • Get latest deployed release details: kubectl get secret <release_version_secret_name> -n <release_version_namespace> -o yaml > release.bak
  • Decode the release object: cat release.bak | grep -oP '(?<=release: ).*' | base64 -d | base64 -d | gzip -d - > release.data.decoded
  • Change API versions of the manifests. Can use any tool (e.g. editor) to make the changes. This is in the manifest field of your decoded release object (release.data.decoded)
  • Encode the release object: cat release.data.decoded | gzip | base64 | base64
  • Replace data.release property value in the deployed release file (release.bak) with the new encoded release object
  • Apply file to namespace: kubectl apply -f release.bak -n <release_version_namespace>
  • Perform a helm upgrade with a version of the chart with supported Kubernetes API versions
  • Add a description in the upgrade, something along the lines to not perform a rollback to a Helm version prior to this current version