Atelet runs only on nodes hosting ateoms (#9)

cmd/atecontroller/main.go

@@ -88,6 +88,14 @@ func main() {
 		os.Exit(1)
 	}
 
+	if err = (&controllers.AteletNodeReconciler{
+		Client: mgr.GetClient(),
+		Scheme: mgr.GetScheme(),
+	}).SetupWithManager(mgr); err != nil {
+		setupLog.Error(err, "unable to create controller", "controller", "AteletNode")
+		os.Exit(1)
+	}
+
 	//+kubebuilder:scaffold:builder
 
 	if err := mgr.AddHealthzCheck("healthz", healthz.Ping); err != nil {

internal/controllers/ateletnode_controller.go

@@ -0,0 +1,167 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package controllers
+
+import (
+	"context"
+	"fmt"
+
+	corev1 "k8s.io/api/core/v1"
+	k8errors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/types"
+	corev1ac "k8s.io/client-go/applyconfigurations/core/v1"
+	ctrl "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/builder"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/handler"
+	"sigs.k8s.io/controller-runtime/pkg/log"
+	"sigs.k8s.io/controller-runtime/pkg/predicate"
+	"sigs.k8s.io/controller-runtime/pkg/reconcile"
+)
+
+const (
+	AteletNodeLabel      = "ate.dev/atelet"
+	AteletNodeLabelValue = "true"
+
+	// Per-pool claim annotation. Full key: ate.dev/claim.<workerpool-uid>.
+	AteletNodeClaimAnnoPrefix = "ate.dev/claim."
+
+	AteletNodeFieldOwner = "atelet-node-controller"
+	PodNodeNameIndex     = "spec.nodeName"
+)
+
+// claimAnnotationKey is the shared claim-annotation format: written by this
+// reconciler, read by the WorkerPool finalizer.
+func claimAnnotationKey(workerPoolUID string) string {
+	return AteletNodeClaimAnnoPrefix + workerPoolUID
+}
+
+type AteletNodeReconciler struct {
+	client.Client
+	Scheme *runtime.Scheme
+}
+
+//+kubebuilder:rbac:groups="",resources=nodes,verbs=get;list;watch;patch
+//+kubebuilder:rbac:groups="",resources=pods,verbs=get;list;watch
+
+func (r *AteletNodeReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
+	return r.reconcileNode(ctx, req.Name)
+}
+
+func (r *AteletNodeReconciler) reconcileNode(ctx context.Context, nodeName string) (ctrl.Result, error) {
+	logger := log.FromContext(ctx).WithValues("node", nodeName)
+
+	// Existence check only — don't let the SSA apply below recreate a deleted Node.
+	if err := r.Get(ctx, types.NamespacedName{Name: nodeName}, &corev1.Node{}); err != nil {
+		if k8errors.IsNotFound(err) {
+			return ctrl.Result{}, nil
+		}
+		return ctrl.Result{}, fmt.Errorf("get node %q: %w", nodeName, err)
+	}
+
+	// Terminating pods still appear here; intentional, so atelet outlives a
+	// draining ateom (the claim drops only once the pod object is gone).
+	podList := &corev1.PodList{}
+	if err := r.List(ctx, podList, client.MatchingFields{PodNodeNameIndex: nodeName}); err != nil {
+		return ctrl.Result{}, fmt.Errorf("list pods on node %q: %w", nodeName, err)
+	}
+
+	poolUIDs := map[string]struct{}{}
+	for i := range podList.Items {
+		pod := &podList.Items[i]
+		if pod.Spec.NodeName != nodeName {
+			continue
+		}
+		// Skip non-ateom pods; the field index is not label-filtered.
+		uid, ok := pod.Labels[WorkerPoolUIDLabelKey]
+		if !ok || uid == "" {
+			continue
+		}
+		poolUIDs[uid] = struct{}{}
+	}
+
+	logger.V(1).Info("reconciling node claims", "pool_count", len(poolUIDs))
+	return ctrl.Result{}, r.applyNodeClaims(ctx, nodeName, poolUIDs)
+}
+
+// applyNodeClaims SSA-applies the label + per-pool claims; keys absent from
+// the apply are pruned by field-ownership (last claim gone -> label removed).
+func (r *AteletNodeReconciler) applyNodeClaims(ctx context.Context, nodeName string, poolUIDs map[string]struct{}) error {
+	nodeAC := corev1ac.Node(nodeName)
+
+	labels := map[string]string{}
+	if len(poolUIDs) > 0 {
+		labels[AteletNodeLabel] = AteletNodeLabelValue
+	}
+	nodeAC.Labels = labels
+
+	annotations := map[string]string{}
+	for uid := range poolUIDs {
+		annotations[claimAnnotationKey(uid)] = ""
+	}
+	nodeAC.Annotations = annotations
+
+	if err := r.Apply(ctx, nodeAC, client.FieldOwner(AteletNodeFieldOwner), client.ForceOwnership); err != nil {
+		return fmt.Errorf("apply node %q: %w", nodeName, err)
+	}
+	return nil
+}
+
+// podToNode maps a Pod event to its assigned Node (none if unscheduled).
+func (r *AteletNodeReconciler) podToNode(_ context.Context, obj client.Object) []reconcile.Request {
+	pod, ok := obj.(*corev1.Pod)
+	if !ok {
+		return nil
+	}
+	if pod.Spec.NodeName == "" {
+		return nil
+	}
+	return []reconcile.Request{{NamespacedName: types.NamespacedName{Name: pod.Spec.NodeName}}}
+}
+
+// ateomPodPredicate admits ateom pods by the UID label — the key reconcileNode
+// consumes — so the watch only fires for pods we can actually refcount.
+func ateomPodPredicate() predicate.Predicate {
+	return predicate.NewPredicateFuncs(func(obj client.Object) bool {
+		labels := obj.GetLabels()
+		if labels == nil {
+			return false
+		}
+		_, ok := labels[WorkerPoolUIDLabelKey]
+		return ok
+	})
+}
+
+// SetupWithManager indexes Pod.Spec.NodeName so reconcileNode can list by node.
+func (r *AteletNodeReconciler) SetupWithManager(mgr ctrl.Manager) error {
+	if err := mgr.GetFieldIndexer().IndexField(context.Background(), &corev1.Pod{}, PodNodeNameIndex, func(o client.Object) []string {
+		p := o.(*corev1.Pod)
+		if p.Spec.NodeName == "" {
+			return nil
+		}
+		return []string{p.Spec.NodeName}
+	}); err != nil {
+		return err
+	}
+	return ctrl.NewControllerManagedBy(mgr).
+		Named("atelet-node").
+		Watches(
+			&corev1.Pod{},
+			handler.EnqueueRequestsFromMapFunc(r.podToNode),
+			builder.WithPredicates(ateomPodPredicate()),
+		).
+		Complete(r)
+}