Chapter 1. Hosted control planes overview

When you use hosted control planes for OpenShift Container Platform, it is important to understand its key concepts and the personas that are involved.

You can use hosted control planes for Red Hat OpenShift Container Platform to reduce management costs, optimize cluster deployment time, and separate management and workload concerns so that you can focus on your applications.

Hosted control planes is available by using the multicluster engine for Kubernetes Operator version 2.0 or later on the following platforms:

1.2.1. Architecture of hosted control planes

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.

You can configure hosted control planes by using the multicluster engine for Kubernetes Operator. The multicluster engine is an integral part of Red Hat Advanced Cluster Management (RHACM) and is enabled by default with RHACM. The multicluster engine Operator cluster lifecycle defines the process of creating, importing, managing, and destroying Kubernetes clusters across various infrastructure cloud providers, private clouds, and on-premises data centers.

The multicluster engine Operator is the cluster lifecycle Operator that provides cluster management capabilities for OpenShift Container Platform and RHACM hub clusters. The multicluster engine Operator enhances cluster fleet management and supports OpenShift Container Platform cluster lifecycle management across clouds and data centers.

Figure 1.1. Cluster life cycle and foundation

You can use the multicluster engine Operator with OpenShift Container Platform as a standalone cluster manager or as part of a RHACM hub cluster.

You can deploy OpenShift Container Platform clusters by using two different control plane configurations: standalone or hosted control planes. The standalone configuration uses dedicated virtual machines or physical machines to host the control plane. With hosted control planes for OpenShift Container Platform, you create control planes as pods on a management cluster without the need for dedicated virtual or physical machines for each control plane.

Figure 1.2. RHACM and the multicluster engine Operator introduction diagram

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":["4.16"]}'
    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 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.