Feature Overview (aka. Goal Summary)  

With on-prem networking (i.e. platform:baremetal or platform:vsphere), all control plane nodes must be in the same subnet, as they share the API VIP that is managed using VRRP. Similarly, all worker nodes must be in the same subnet because they share the Ingress VIP in the same way.

However, there is no reason in principle that the control plane machine subnet and the worker machine subnet need to be the same subnet.

Goals (aka. expected user outcomes)

Allow the API and Ingress VIPs to belong to different subnets.

Requirements (aka. Acceptance Criteria):

• Must work in all of Metal IPI, Assisted, ABI, and ZTP installers
• Verifiable in dev-scripts
• Exercised by at least a periodic CI job
   

  Deployment considerations	List applicable specific needs (N/A = not applicable)
  Self-managed, managed, or both	Self-managed
  Classic (standalone cluster)	Yes
  Hosted control planes	N/A
  Multi node, Compact (three node), or Single node (SNO), or all	HA
  Connected / Restricted Network	N/A
  Architectures, e.g. x86_x64, ARM (aarch64), IBM Power (ppc64le), and IBM Z (s390x)	N/A
  Operator compatibility	N/A
  Backport needed (list applicable versions)	N/A
  UI need (e.g. OpenShift Console, dynamic plugin, OCM)	N/A
  Other (please specify)

  Use Cases (Optional):

Include use case diagrams, main success scenarios, alternative flow scenarios.  Initial completion during Refinement status.

<your text here>

Questions to Answer (Optional):

Out of Scope

Handling topologies where worker nodes are not in the same subnet as each other is out of scope for this Feature.

Background

Reportedly, baremetal-runtimecfg contains a number of assumptions that the Ingress and API VIPs are part of the same subnet. Customers have reportedly tried putting them in different subnets without success.

OCPBUGS-30730 contains information about what would be needed in assisted-service to ensure that validations pass in Assisted/ABI/ZTP, assuming that this were fundamentally possible in OpenShift. (However, the ticket is closed since currently it is not.)

Customer Considerations

Documentation Considerations

Both the baremetal IPI and ABI documentation will need to be updated.

Interoperability Considerations