[release-4.20] OCPBUGS-59766: Update timing of MCN desired config spec update to align with node annotation setting

pkg/controller/node/node_controller.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	helpers "github.com/openshift/machine-config-operator/pkg/helpers"
+	"github.com/openshift/machine-config-operator/pkg/upgrademonitor"
 
 	configv1 "github.com/openshift/api/config/v1"
 	features "github.com/openshift/api/features"
@@ -1288,14 +1289,16 @@ func (ctrl *Controller) updateCandidateNode(mosc *mcfgv1.MachineOSConfig, mosb *
 		}
 
 		lns := ctrlcommon.NewLayeredNodeState(oldNode)
+		desiredConfig := ""
 		if !layered {
 			lns.SetDesiredStateFromPool(pool)
+			desiredConfig = pool.Spec.Configuration.Name
 		} else {
 			lns.SetDesiredStateFromMachineOSConfig(mosc, mosb)
+			desiredConfig = mosb.Spec.MachineConfig.Name
 		}
 
 		// Set the desired state to match the pool.
-
 		newData, err := json.Marshal(lns.Node())
 		if err != nil {
 			return err
@@ -1306,6 +1309,12 @@ func (ctrl *Controller) updateCandidateNode(mosc *mcfgv1.MachineOSConfig, mosb *
 			return nil
 		}
 
+		// Populate the desired config version and image annotations in the node's MCN
+		err = upgrademonitor.UpdateMachineConfigNodeSpecDesiredAnnotation(ctrl.fgHandler, ctrl.client, nodeName, desiredConfig)
+		if err != nil {
+			klog.Errorf("error populating MCN for desired config version and image updates: %v", err)
+		}
+
 		klog.V(4).Infof("Pool %s: layered=%v node %s update is needed", pool.Name, layered, nodeName)
 		patchBytes, err := strategicpatch.CreateTwoWayMergePatch(oldData, newData, corev1.Node{})
 		if err != nil {

pkg/upgrademonitor/upgrade_monitor.go

@@ -335,6 +335,42 @@ func isSingletonCondition(singletonConditionTypes []mcfgv1.StateProgress, condit
 	return false
 }
 
+// UpdateMachineConfigNodeSpecDesiredAnnotation sets the desired config version in the `Spec` of an
+// existing MachineConfigNode resource
+func UpdateMachineConfigNodeSpecDesiredAnnotation(fgHandler ctrlcommon.FeatureGatesHandler, mcfgClient mcfgclientset.Interface, nodeName, desiredConfig string) error {
+	if fgHandler == nil {
+		return nil
+	}
+
+	// Check that the MachineConfigNode feature gate is enabled
+	if !fgHandler.Enabled(features.FeatureGateMachineConfigNodes) {
+		klog.Infof("MachineConfigNode FeatureGate is not enabled.")
+		return nil
+	}
+
+	// Get the existing MCN
+	mcn, mcnErr := mcfgClient.MachineconfigurationV1().MachineConfigNodes().Get(context.TODO(), nodeName, metav1.GetOptions{})
+	// Note that this function is only intended to update the Spec of an existing MCN. We should
+	// not reach this point if there is not an existing MCN for a node, but we need to handle the
+	// DNE and other potential error situations just in case.
+	if mcnErr != nil {
+		return mcnErr
+	}
+
+	// Set the desired config annotation
+	mcn.Spec.ConfigVersion.Desired = NotYetSet
+	if desiredConfig != "" {
+		mcn.Spec.ConfigVersion.Desired = desiredConfig
+	}
+
+	// Update the MCN resource
+	if _, err := mcfgClient.MachineconfigurationV1().MachineConfigNodes().Update(context.TODO(), mcn, metav1.UpdateOptions{FieldManager: "machine-config-operator"}); err != nil {
+		return fmt.Errorf("failed to update the %s mcn spec with the new desired config value: %w", nodeName, err)
+	}
+
+	return nil
+}
+
 // GenerateAndApplyMachineConfigNodeSpec generates and applies a new MCN spec based off the node state
 func GenerateAndApplyMachineConfigNodeSpec(fgHandler ctrlcommon.FeatureGatesHandler, pool string, node *corev1.Node, mcfgClient mcfgclientset.Interface) error {
 	if fgHandler == nil || node == nil {