Description
  Validate feasibility of introducing OSImageStream to MCO, enabling per-pool OS image stream selection from release metadata.

Outcome

Stream Extraction from Release Image

• Successfully extracts ImageStream from /release-manifests/image-references in release image layers
• Parses image labels (io.coreos.oscontainerimage.osstream) to identify stream associations
• Groups OS/Extensions images by stream name
• Implementation: pkg/controller/osimagestream/imagestream_provider.go, imagestream_osimages.go

Multiple Source Support

• Three sources with precedence: CLI args → ImageStream → ConfigMap
• StreamSource interface allows composition and merging
• Maintains backward compatibility with existing machine-config-osimageurl ConfigMap
• Implementation: pkg/controller/osimagestream/osimagestream.go

API Design

• v1alpha1 singleton OSImageStream resource (name: "cluster")
• Status-driven: operator populates available streams, users select via MachineConfigPool
• Feature-gated behind OSStreams
• Added spec.osImageStream field to MachineConfigPool

PR: https://github.com/openshift/machine-config-operator/pull/5381