operator: update control plane nodes first

operators/constellation-node-operator/controllers/nodeversion_controller.go

@@ -11,6 +11,7 @@ import (
 	"encoding/json"
 	"errors"
 	"reflect"
+	"slices"
 	"strings"
 	"time"
 
@@ -388,6 +389,10 @@ func (r *NodeVersionReconciler) tryStartClusterVersionUpgrade(ctx context.Contex
 func (r *NodeVersionReconciler) pairDonorsAndHeirs(ctx context.Context, controller metav1.Object, outdatedNodes []corev1.Node, mintNodes []mintNode) []replacementPair {
 	logr := log.FromContext(ctx)
 	var pairs []replacementPair
+
+	// Prioritize control-plane nodes, which need to be upgraded first starting with k8s v1.31.0.
+	sortByControlPlanes(outdatedNodes)
+
 	for _, mintNode := range mintNodes {
 		var foundReplacement bool
 		// find outdated node in the same group
@@ -943,3 +948,16 @@ type newNodeConfig struct {
 	scalingGroupByID   map[string]updatev1alpha1.ScalingGroup
 	newNodesBudget     int
 }
+
+func sortByControlPlanes(nodes []corev1.Node) {
+	slices.SortStableFunc(nodes, func(a, b corev1.Node) int {
+		_, aControlPlane := a.Labels["node-role.kubernetes.io/control-plane"]
+		_, bControlPlane := b.Labels["node-role.kubernetes.io/control-plane"]
+		if aControlPlane == bControlPlane {
+			return 0
+		} else if aControlPlane {
+			return -1
+		}
+		return 1
+	})
+}

operators/constellation-node-operator/controllers/nodeversion_controller_test.go

@@ -9,6 +9,7 @@ package controllers
 import (
 	"context"
 	"errors"
+	"fmt"
 	"sync"
 	"testing"
 
@@ -891,3 +892,42 @@ func (*unimplementedNodeReplacer) CreateNode(_ context.Context, _ string) (nodeN
 func (*unimplementedNodeReplacer) DeleteNode(_ context.Context, _ string) error {
 	panic("unimplemented")
 }
+
+func TestSortByControlPlane(t *testing.T) {
+	w1 := newNode("w1", false)
+	w2 := newNode("w2", false)
+	cp1 := newNode("cp1", true)
+	cp2 := newNode("cp2", true)
+
+	for i, tc := range []struct {
+		input    []corev1.Node
+		expected []string
+	}{
+		{input: []corev1.Node{w1, w2, cp1, cp2}, expected: []string{"cp1", "cp2", "w1", "w2"}},
+		{input: []corev1.Node{w2, cp1, cp2, w1}, expected: []string{"cp1", "cp2", "w2", "w1"}},
+		{input: []corev1.Node{cp2, w1, cp1, w2}, expected: []string{"cp2", "cp1", "w1", "w2"}},
+		{input: []corev1.Node{cp1, cp2, w1, w2}, expected: []string{"cp1", "cp2", "w1", "w2"}},
+	} {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			sortByControlPlanes(tc.input)
+			var actual []string
+			for _, node := range tc.input {
+				actual = append(actual, node.Name)
+			}
+			assert.Equal(t, tc.expected, actual)
+		})
+	}
+}
+
+func newNode(name string, controlPlane bool) corev1.Node {
+	node := corev1.Node{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:   name,
+			Labels: make(map[string]string),
+		},
+	}
+	if controlPlane {
+		node.Labels["node-role.kubernetes.io/control-plane"] = ""
+	}
+	return node
+}