Feature Overview (aka. Goal Summary)  

As a cluster administrator I need ROSA to support subnets smaller than /25 (single-az) or /24 (multi-az) so that I can create clusters of small sizes that run workloads that do not scale horizontally (e.g., traditional databases installed through CP4D) and that installs in micro-segmented network infrastructure, I

Goals (aka. expected user outcomes)

Currently, our documented supported configurations are

A minimum IP address range of 128 addresses, using the subnet prefix /25, is supported for single availability zone deployments. A minimum address range of 256 addresses, using the subnet prefix /24, is supported for deployments that use multiple availability zones.

Source: https://docs.openshift.com/rosa/networking/cidr-range-definitions.html#machine-cidr-description

 The goal is to be able to support subnets with a smaller number IP addresses

Requirements (aka. Acceptance Criteria):

• Successfully deploy a cluster with smaller subnet CIDR ranges
• Validate that we know the minimums for single-az and multi-az configurations in ROSA Classic
• Validate that the single-az minimum equally applies to ROSA HCP
• Enforce this is only applicable in BYO-VPC scenarios
• Update necessary preflight checks
• Update necessary documentation
• Perform any validation or IP address reservation necessary to ensure that SREP can get access into a subnet (jump host, etc) if needed
• Determine the minimum number of required IP's for non-machine related purposes, e.g., load balancers, etc