User Story:

As a (user persona), I want to be able to:

• Create IPI AWS clusters with Public IP-only option (aka. NAT-less deployment) with managed-VPC

so that I can achieve

• significant cost saving for OpenShift CI

Currently, openshift-installer supports "OPENSHIFT_INSTALL_AWS_PUBLIC_ONLY" environment, which will skip creating NAT Gateway. However, the above env will make openshift-installer skip the entire creation of VPC, which means, the VPC must be manually created beforehand. Our goal is to modify the behaviour of "OPENSHIFT_INSTALL_AWS_PUBLIC_ONLY" to allow omitting "subnets" section in install config and let the openshift-installer to create the VPC and Internet Gateway (in replacement of NAT Gateway).

Acceptance Criteria:

Description of criteria:

• Passing "OPENSHIFT_INSTALL_AWS_PUBLIC_ONLY" without "subnets" section in install config will not report:

  level=error msg=failed to fetch Master Machines: failed to load asset "Install Config": failed to create install config: platform.aws.subnets: Required value: subnets must be specified for public-only subnets clusters
  

(optional) Out of Scope:

Detail about what is specifically not being delivered in the story

Engineering Details:

• (optional) https://github/com/link.to.enhancement/
• (optional) https://issues.redhat.com/link.to.spike
• Engineering detail 1
• Engineering detail 2

This requires/does not require a design proposal.
This requires/does not require a feature gate.