Chapter 2. Hosted control planes overview

OpenShift Container Platform is often deployed in a coupled, or standalone, model, where a cluster consists of a control plane and a data plane. The control plane includes an API endpoint, a storage endpoint, a workload scheduler, and an actuator that ensures state. The data plane includes compute, storage, and networking where workloads and applications run.

The standalone control plane is hosted by a dedicated group of nodes, which can be physical or virtual, with a minimum number to ensure quorum. The network stack is shared. Administrator access to a cluster offers visibility into the cluster’s control plane, machine management APIs, and other components that contribute to the state of a cluster.

Although the standalone model works well, some situations require an architecture where the control plane and data plane are decoupled. In those cases, the data plane is on a separate network domain with a dedicated physical hosting environment. The control plane is hosted by using high-level primitives such as deployments and stateful sets that are native to Kubernetes. The control plane is treated as any other workload.

With hosted control planes, you can pave the way for a true hybrid-cloud approach and enjoy several other benefits.

In management clusters for production use, you need multicluster engine for Kubernetes Operator, which is available through OperatorHub. The multicluster engine Operator bundles a supported build of the HyperShift Operator. For your management clusters to remain supported, you must use the version of OpenShift Container Platform that multicluster engine Operator runs on. In general, a new release of multicluster engine Operator runs on the following versions of OpenShift Container Platform:

The full list of OpenShift Container Platform versions that you can install through the HyperShift Operator on a management cluster depends on the version of your HyperShift Operator. However, the list always includes at least the same OpenShift Container Platform version as the management cluster and two previous minor versions relative to the management cluster. For example, if the management cluster is running 4.17 and a supported version of multicluster engine Operator, the HyperShift Operator can install 4.17, 4.16, 4.15, and 4.14 hosted clusters.

With each major, minor, or patch version release of OpenShift Container Platform, two components of hosted control planes are released:

The HyperShift Operator manages the lifecycle of hosted clusters that are represented by the HostedCluster API resources. The HyperShift Operator is released with each OpenShift Container Platform release. The HyperShift Operator creates the supported-versions config map in the hypershift namespace. The config map contains the supported hosted cluster versions.

You can host different versions of control planes on the same management cluster.

    apiVersion: v1
    data:
      supported-versions: '{"versions":["4.17"]}'
    kind: ConfigMap
    metadata:
      labels:
        hypershift.openshift.io/supported-versions: "true"
      name: supported-versions
      namespace: hypershift

You can use the hcp CLI to create hosted clusters. You can download the CLI from multicluster engine Operator. When you run the hcp version command, the output shows the latest OpenShift Container Platform that the CLI supports against your kubeconfig file.

You can use the hypershift.openshift.io API resources, such as, HostedCluster and NodePool, to create and manage OpenShift Container Platform clusters at scale. A HostedCluster resource contains the control plane and common data plane configuration. When you create a HostedCluster resource, you have a fully functional control plane with no attached nodes. A NodePool resource is a scalable set of worker nodes that is attached to a HostedCluster resource.

The API version policy generally aligns with the policy for Kubernetes API versioning.

Updates for hosted control planes involve updating the hosted cluster and the node pools. For more information, see "Updates for hosted control planes".

The Control Plane Operator is released as part of each OpenShift Container Platform payload release image for the following architectures: