Cluster API Version Support and Kubernetes Version Skew Policy

Supported Versions

The Cluster API team maintains branches for v1.x (v1beta1) v0.4 (v1alpha4) and v0.3 (v1alpha3), the most recent releases.

Releases include these components:

• Core Provider
• Kubeadm Bootstrap Provider
• Kubeadm Control Plane Provider
• clusterctl client

All Infrastructure Providers are maintained by independent teams. Other Bootstrap and Control Plane Providers are also maintained by independent teams. For more information about their version support, see below.

Supported Kubernetes Versions

The project aims to keep the current minor release compatible with the actively supported Kubernetes minor releases, i.e., the current release (N), N-1, and N-2. Where possible we will go above and beyond this trying to help our users support both newer and older versions of Kubernetes:

• For a given Cluster API minor release, we give best-effort support for future Kubernetes versions that are released during the release’s active support period. Depending on the changes made in Kubernetes, users may be required to update to the next patch release of Cluster API to maintain compatibility.
• In some cases where support for future Kubernetes versions can’t be added, or is considered not practical or too risky adding it, the Kubernetes version support matrix for an existing Cluster API minor release will stop at the last supported version.
• Cluster API offers best-effort support for older Kubernetes versions where possible. Important! this is not a replacement/alternative for upstream Kubernetes support policies! Support for older version of Kubernetes is limited to “Cluster API can start a Cluster with this Kubernetes version” and “Cluster API can upgrade to the next Kubernetes version”; it does not include any extended support to Kubernetes itself.

Whenever a new Cluster API release is cut, we will document the Kubernetes version compatibility matrix the release has been tested with. Summaries of Kubernetes versions supported by each component are additionally maintained in the tables below.

On a final comment, let’s praise all the contributors keeping care of such a wide support matrix. If someone is looking for opportunities to help with the project, this is definitely an area where additional hands and eyes will be more than welcome and greatly beneficial to the entire community.

See the following section to understand how cluster topology affects version support.

Kubernetes Version Support As A Function Of Cluster Topology

The Core Provider, Kubeadm Bootstrap Provider, and Kubeadm Control Plane Provider run on the Management Cluster, and clusterctl talks to that cluster’s API server.

In some cases, the Management Cluster is separate from the Workload Clusters. The Kubernetes version of the Management and Workload Clusters are allowed to be different.

Management Clusters and Workload Clusters can be upgraded independently and in any order, however, if you are additionally moving from v1alpha3 (v0.3.x) to v1beta1 (v1.x) as part of the upgrade rollout, the management cluster will need to be upgraded to at least v1.19.x, prior to upgrading any workload cluster using Cluster API v1beta1 (v1.x)

These diagrams show the relationships between components in a Cluster API release (yellow), and other components (white).

Management And Workload Cluster Are the Same (Self-hosted)

Management And Workload Clusters Are Separate

Release Components

Core Provider (cluster-api-controller)

* There is an issue with CRDs in Kubernetes v1.23.{0-2}. ClusterClass with patches is affected by that (for more details please see this issue). Therefore we recommend to use Kubernetes v1.23.3+ with ClusterClass. Previous Kubernetes minor versions are not affected.

The Core Provider also talks to API server of every Workload Cluster. Therefore, the Workload Cluster’s Kubernetes version must also be compatible.

Kubeadm Bootstrap Provider (kubeadm-bootstrap-controller)

The Kubeadm Bootstrap Provider generates kubeadm configuration using the API version recommended for the target Kubernetes version.

Kubeadm Control Plane Provider (kubeadm-control-plane-controller)

The Kubeadm Control Plane Provider talks to the API server and etcd members of every Workload Cluster whose control plane it owns. It uses the etcd v3 API.

The Kubeadm Control Plane requires the Kubeadm Bootstrap Provider.

* Newer versions of CoreDNS may not be compatible as an upgrade target for clusters managed with Cluster API. Kubernetes versions marked on the table are supported as an upgrade target only if CoreDNS is not upgraded to the latest version supported by the respective Kubernetes version. The versions supported are represented in the below table.

Kubernetes version specific notes

1.24:

• Kubeadm Bootstrap Provider:
  • kubeadm now sets both the node-role.kubernetes.io/control-plane and node-role.kubernetes.io/master taints on control plane nodes.
  • kubeadm now only sets the node-role.kubernetes.io/control-plane label on control plane nodes (the node-role.kubernetes.io/master label is not set anymore).
• Kubeadm Bootstrap Provider and Kubeadm Control Plane Provider
  • criSocket without a scheme prefix has been deprecated in the kubelet since a while. kubeadm now shows a warning if no scheme is present and eventually the support for criSocket‘s without prefix will be dropped. Please adjust the criSocket accordingly (e.g. unix:///var/run/containerd/containerd.sock) if you are configuring the criSocket in CABPK or KCP resources.

clusterctl

It is strongly recommended to always use the latest version of clusterctl, in order to get all the fixes/latest changes.

In case of upgrades, clusterctl should be upgraded first and then used to upgrade all the other components.

Providers Maintained By Independent Teams

In general, if a Provider version M says it is compatible with Cluster API version N, then version M must be compatible with a subset of the Kubernetes versions supported by Cluster API version N.

To understand the version compatibility of a specific provider, please see its documentation. This book includes a list of independent providers