MCO-1927: Add osImageStream to MCPs

Adds the osImageStream field to MachineConfigPoolSpec, allowing individual
pools to override cluster-wide OS images with a specific OS stream.

The field is optional and gated behind the OSStreams feature gate. When
omitted, pools use the cluster-wide default OS images.

Author: pablintino

machineconfiguration/v1/tests/machineconfigpools.machineconfiguration.openshift.io/OSStreams.yaml

@@ -0,0 +1,78 @@
+apiVersion: apiextensions.k8s.io/v1 # Hack because controller-gen complains if we don't have this
+name: "[TechPreview] OSStreams"
+crdName: machineconfigpools.machineconfiguration.openshift.io
+featureGates:
+- OSStreams
+tests:
+  onCreate:
+    - name: Should be able to create a minimal MachineConfigPool
+      initial: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec: {} # No spec is required for a MachineConfigPool
+      expected: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec: {}
+    - name: Should be able to select a non-default osImageStream
+      initial: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: "rhel10-coreos"
+      expected: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: "rhel10-coreos"
+    - name: If given, the osImageStream must be non-empty
+      initial: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: ""
+      expectedError: "spec.osImageStream in body should be at least 1 chars long"
+    - name: If given, the osImageStream should be composed only by alphanumeric chars, hyphens and dots
+      initial: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: "rhel10#1-coreos"
+      expectedError: "spec.osImageStream: Invalid value: \"string\": The osImageStream must start with a letter and contain only alphanumeric characters, hyphens ('-'), and dots ('.')."
+    - name: If given, the osImageStream should not exceed 70 characters
+      initial: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: "rhel-coreos32131e2ddf34f44r3r3r4f43tg54frg54tg45454g4g45gt34f43g54g45g3"
+      expectedError: "Too long: may not be more than 70 bytes"
+  onUpdate:
+    - name: If given, the osImageStream can be removed
+      initial: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: "rhel10-coreos"
+      updated: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec: {}
+      expected: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec: {}
+    - name: If not present, the osImageStream can be added to the pool
+      initial: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec: {}
+      updated: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: "rhel10-coreos"
+      expected: |
+        apiVersion: machineconfiguration.openshift.io/v1
+        kind: MachineConfigPool
+        spec:
+          osImageStream: "rhel10-coreos"

machineconfiguration/v1/types.go

@@ -452,6 +452,22 @@ type MachineConfigPoolSpec struct {
 	// +listMapKey=name
 	// +kubebuilder:validation:MaxItems=100
 	PinnedImageSets []PinnedImageSetRef `json:"pinnedImageSets,omitempty"`
+
+	// osImageStream specifies an OS stream to be used for the pool.
+	//
+	// When set, this value overrides the cluster-wide OS images for the pool with
+	// the OS and Extensions associated to the specified stream.
+	// When omitted or empty, the pool uses the cluster-wide default OS images.
+	//
+	// The stream name must start with a letter and contain only alphanumeric
+	// characters, hyphens ('-'), and dots ('.'), with a maximum length of 70 characters.
+	//
+	// +optional
+	// +openshift:enable:FeatureGate=OSStreams
+	// +kubebuilder:validation:MinLength=1
+	// +kubebuilder:validation:MaxLength=70
+	// +kubebuilder:validation:XValidation:rule=`self.matches('^[a-zA-Z][a-zA-Z0-9.-]*$')`,message="The osImageStream must start with a letter and contain only alphanumeric characters, hyphens ('-'), and dots ('.')."
+	OSImageStream string `json:"osImageStream,omitempty"`
 }
 
 type PinnedImageSetRef struct {