Feature Overview (aka. Goal Summary)  

This feature aims to enable customers to deploy Hosted Control Planes (HCP) in compact OpenShift cluster setups. The primary goal is to be comfortable supporting at least 1 to 3 hosted alongside standalone masters.

This feature addresses customer demand for more efficient resource utilization in constrained or specialized deployments, or in environments where little nodes with a lot of compute resources available to ensure better utilization.

Goals (aka. expected user outcomes)

Be comfortable supporting 1 Hosted control plane hosted in a compact setup (to communicate the in docs). I.e., we will test with 1 on compact cluster, but any other growth will be subject to ability to elastically scale or subject to local risk on number of HA workloads would be required.  So 1 is not a ceiling.

Requirements (aka. Acceptance Criteria):

QE

• We will need to QE this setup for the following:
• There are no issues running HCP alongside OCP masters (schedulable)
• The compact management clusters can be upgraded alongside HCP
• HCP can be upgraded without impact on the management cluster
• Remediation steps from when a node goes down (e.g., https://docs.openshift.com/container-platform/4.15/hosted_control_planes/hcp-backup-restore-dr.html#hosted-cluster-etcd-backup-restore-on-prem_hcp-backup-restore-dr_

Perf/Scale (sizing): 

• We will need to make sure we update the sizing guidance to consider static masters and give preliminary sizing.

Documentation

• We will need to document constraints such as:

• • Nothing else can be deployed on the compact cluster beyond HCPs
  • The workload is not demanding. Falls within a low QPS profile (e.g., https://github.com/zanetworker/hcp-sizer?tab=readme-ov-file#qps-categories)

Use Cases (Optional):

As a service provider with very large baremetal machines and not so many of them, I would like to better utilize existing resources by sharing infra between standalone masters and hosted control planes.

As a service provider wanting to implement more secure boundaries between my applications and my management plane, I wanted to use Hosted control planes on a pre-existing compact infrastructure.

Questions to Answer (Optional):

Include a list of refinement / architectural questions that may need to be answered before coding can begin.  Initial completion during Refinement status.

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Out of Scope

Deployment of more than 3 HCPs in a compact cluster configuration. For additional control-planes, customers can add more workers to the cluster.

Background

The push for deploying HCPs in compact OpenShift clusters arises from the need to better utilize resources in constrained environments, where deploying large clusters is not feasible or cost-effective.

Customer Considerations

• Customers must ensure their infrastructure can support the added load of HCPs in compact clusters.
• Understanding the limitations and best practices for deploying HCPs in such environments is crucial for success.

Documentation Considerations

• Update existing OpenShift documentation to include guidance on deploying HCPs in compact clusters.
• [Bonus] Provide troubleshooting guides and best practices specifically for compact HCP deployments.