[CASCL-1386] Create temporary PodDisruptionBudgets during eviction

Part of a stack splitting #3026 (too large to review in one piece) into
small pieces that each build and pass tests on their own. The command is
fully functional only once the whole stack lands.

Author: L3n41c

cmd/kubectl-datadog/autoscaling/cluster/evict/pdb.go

@@ -2,15 +2,335 @@ package evict
 
 import (
 	"context"
+	"errors"
+	"fmt"
+	"log"
+	"reflect"
+	"slices"
+	"strings"
 
+	"github.com/samber/lo"
+	appsv1 "k8s.io/api/apps/v1"
+	corev1 "k8s.io/api/core/v1"
+	policyv1 "k8s.io/api/policy/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/util/intstr"
+	"k8s.io/apimachinery/pkg/util/validation"
 	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/tools/pager"
 	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	commonk8s "github.com/DataDog/datadog-operator/cmd/kubectl-datadog/autoscaling/cluster/common/k8s"
+)
+
+// Label keys used to mark PodDisruptionBudgets created by this command. Both
+// must be present for cleanup to consider the PDB ours — this makes the
+// cleanup safe against accidentally removing a user PDB with a colliding name.
+const (
+	pdbManagedByLabelKey   = "app.kubernetes.io/managed-by"
+	pdbManagedByLabelValue = "kubectl-datadog"
+	pdbTempLabelKey        = "autoscaling.datadoghq.com/temporary-pdb"
+	pdbTempLabelValue      = "true"
+	// pdbNameSuffix is appended to the controller name to form the temp PDB
+	// name.
+	pdbNameSuffix = "-evict-legacy"
 )
 
 func ensureTempPDBs(ctx context.Context, clientset kubernetes.Interface, ctrlClient client.Client, targets []Target, dryRun bool) error {
-	panic("TODO: ensureTempPDBs — implemented in PR https://github.com/DataDog/datadog-operator/pull/3178")
+	allNodes := lo.FlatMap(targets, func(t Target, _ int) []string { return t.Nodes })
+	nodeSet := lo.SliceToMap(allNodes, func(n string) (string, struct{}) { return n, struct{}{} })
+	if len(nodeSet) == 0 {
+		return nil
+	}
+
+	controllers, err := discoverControllers(ctx, clientset, nodeSet)
+	if err != nil {
+		return fmt.Errorf("failed to discover controllers: %w", err)
+	}
+	if len(controllers) == 0 {
+		return nil
+	}
+
+	// Group controllers by namespace to amortize the per-namespace PDB list.
+	byNamespace := make(map[string][]controllerInfo)
+	for _, c := range controllers {
+		byNamespace[c.Namespace] = append(byNamespace[c.Namespace], c)
+	}
+
+	var errs []error
+	for ns, ctrls := range byNamespace {
+		existing, err := listNamespacePDBs(ctx, clientset, ns)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("namespace %s: failed to list PDBs: %w", ns, err))
+			continue
+		}
+		for _, c := range ctrls {
+			if hasUserPDB(existing, c.Selector) {
+				continue
+			}
+			if err := createTempPDB(ctx, ctrlClient, c, dryRun); err != nil {
+				errs = append(errs, fmt.Errorf("controller %s/%s/%s: %w", c.Namespace, c.Kind, c.Name, err))
+			}
+		}
+	}
+	return errors.Join(errs...)
 }
 
 func cleanupTempPDBs(ctx context.Context, ctrlClient client.Client, dryRun bool) error {
-	panic("TODO: cleanupTempPDBs — implemented in PR https://github.com/DataDog/datadog-operator/pull/3178")
+	list := &policyv1.PodDisruptionBudgetList{}
+	if err := ctrlClient.List(ctx, list, client.MatchingLabels{
+		pdbManagedByLabelKey: pdbManagedByLabelValue,
+		pdbTempLabelKey:      pdbTempLabelValue,
+	}); err != nil {
+		return fmt.Errorf("failed to list temporary PDBs: %w", err)
+	}
+	if len(list.Items) == 0 {
+		return nil
+	}
+	var errs []error
+	for i := range list.Items {
+		pdb := &list.Items[i]
+		if dryRun {
+			log.Printf("[dry-run] would delete PDB %s/%s", pdb.Namespace, pdb.Name)
+			continue
+		}
+		if err := commonk8s.Delete(ctx, ctrlClient, pdb); err != nil {
+			errs = append(errs, fmt.Errorf("PDB %s/%s: %w", pdb.Namespace, pdb.Name, err))
+		}
+	}
+	return errors.Join(errs...)
+}
+
+// controllerKey identifies a top-level controller that owns evictable pods on
+// our target nodes. It is the dedup key in the seen map and the identity half
+// of controllerInfo.
+type controllerKey struct {
+	Namespace string
+	Kind      string // "Deployment", "StatefulSet", "ReplicaSet"
+	Name      string
+}
+
+// controllerInfo is a controllerKey plus the controller's pod selector — what a
+// PDB would match on.
+type controllerInfo struct {
+	controllerKey
+	Selector *metav1.LabelSelector
+}
+
+// discoverControllers lists every Pod cluster-wide once (paginated) and, for
+// each Pod scheduled on one of the target nodes, resolves the top-level
+// controller. Listing once and filtering client-side avoids the N-API-calls
+// problem of doing one List per node, which on a large legacy fleet would
+// dominate the command's wall-clock time. The resulting slice contains each
+// controller at most once.
+func discoverControllers(ctx context.Context, clientset kubernetes.Interface, nodeSet map[string]struct{}) ([]controllerInfo, error) {
+	seen := make(map[controllerKey]*metav1.LabelSelector)
+	depCache := make(map[client.ObjectKey]*appsv1.Deployment)
+	rsCache := make(map[client.ObjectKey]*appsv1.ReplicaSet)
+	stsCache := make(map[client.ObjectKey]*appsv1.StatefulSet)
+
+	p := pager.New(func(ctx context.Context, opts metav1.ListOptions) (runtime.Object, error) {
+		return clientset.CoreV1().Pods(metav1.NamespaceAll).List(ctx, opts)
+	})
+	if err := p.EachListItem(ctx, metav1.ListOptions{}, func(obj runtime.Object) error {
+		pod := obj.(*corev1.Pod)
+		if _, onTarget := nodeSet[pod.Spec.NodeName]; !onTarget {
+			return nil
+		}
+		if shouldSkipEviction(pod) {
+			return nil
+		}
+		info, err := resolveTopLevelController(ctx, clientset, pod, depCache, rsCache, stsCache)
+		if err != nil {
+			log.Printf("Warning: cannot resolve controller for pod %s/%s: %v", pod.Namespace, pod.Name, err)
+			return nil
+		}
+		if info == nil {
+			return nil
+		}
+		seen[info.controllerKey] = info.Selector
+		return nil
+	}); err != nil {
+		return nil, fmt.Errorf("list pods: %w", err)
+	}
+
+	return lo.MapToSlice(seen, func(key controllerKey, selector *metav1.LabelSelector) controllerInfo {
+		return controllerInfo{controllerKey: key, Selector: selector}
+	}), nil
+}
+
+// resolveTopLevelController walks a Pod's owner chain up to the workload
+// controller (Deployment > ReplicaSet > Pod, StatefulSet > Pod). Returns nil
+// for Pods whose top-level owner is not a stable workload — Jobs (TTL-managed),
+// DaemonSets (already skipped at eviction), or bare Pods.
+func resolveTopLevelController(
+	ctx context.Context,
+	clientset kubernetes.Interface,
+	pod *corev1.Pod,
+	depCache map[client.ObjectKey]*appsv1.Deployment,
+	rsCache map[client.ObjectKey]*appsv1.ReplicaSet,
+	stsCache map[client.ObjectKey]*appsv1.StatefulSet,
+) (*controllerInfo, error) {
+	owner := metav1.GetControllerOf(pod)
+	if owner == nil {
+		return nil, nil
+	}
+	switch owner.Kind {
+	case "ReplicaSet":
+		rs, err := getCached(ctx, rsCache, pod.Namespace, owner.Name, clientset.AppsV1().ReplicaSets(pod.Namespace).Get)
+		if err != nil {
+			return nil, err
+		}
+		rsOwner := metav1.GetControllerOf(rs)
+		if rsOwner != nil && rsOwner.Kind == "Deployment" {
+			dep, err := getCached(ctx, depCache, pod.Namespace, rsOwner.Name, clientset.AppsV1().Deployments(pod.Namespace).Get)
+			if err != nil {
+				return nil, err
+			}
+			return &controllerInfo{
+				controllerKey: controllerKey{Namespace: pod.Namespace, Kind: "Deployment", Name: dep.Name},
+				Selector:      dep.Spec.Selector,
+			}, nil
+		}
+		return &controllerInfo{
+			controllerKey: controllerKey{Namespace: pod.Namespace, Kind: "ReplicaSet", Name: rs.Name},
+			Selector:      rs.Spec.Selector,
+		}, nil
+	case "StatefulSet":
+		sts, err := getCached(ctx, stsCache, pod.Namespace, owner.Name, clientset.AppsV1().StatefulSets(pod.Namespace).Get)
+		if err != nil {
+			return nil, err
+		}
+		return &controllerInfo{
+			controllerKey: controllerKey{Namespace: pod.Namespace, Kind: "StatefulSet", Name: sts.Name},
+			Selector:      sts.Spec.Selector,
+		}, nil
+	default:
+		// DaemonSet (skipped before reaching here), Job (TTL), CronJob,
+		// custom controllers — none get a temporary PDB.
+		return nil, nil
+	}
+}
+
+// getCached returns the object identified by (ns, name) from cache, fetching it
+// via get — the namespace-bound typed clientset accessor, e.g.
+// clientset.AppsV1().ReplicaSets(ns).Get — and populating the cache on a miss.
+// T is inferred from the cache's value type, collapsing the per-kind getters
+// into a single generic lookup.
+func getCached[T any](
+	ctx context.Context,
+	cache map[client.ObjectKey]*T,
+	ns, name string,
+	get func(ctx context.Context, name string, opts metav1.GetOptions) (*T, error),
+) (*T, error) {
+	key := client.ObjectKey{Namespace: ns, Name: name}
+	if obj, ok := cache[key]; ok {
+		return obj, nil
+	}
+	obj, err := get(ctx, name, metav1.GetOptions{})
+	if err != nil {
+		return nil, err
+	}
+	cache[key] = obj
+	return obj, nil
+}
+
+// listNamespacePDBs returns every PDB in the namespace. Used to detect
+// pre-existing user PDBs covering a controller we'd otherwise PDB-protect.
+func listNamespacePDBs(ctx context.Context, clientset kubernetes.Interface, namespace string) ([]policyv1.PodDisruptionBudget, error) {
+	list, err := clientset.PolicyV1().PodDisruptionBudgets(namespace).List(ctx, metav1.ListOptions{})
+	if err != nil {
+		return nil, err
+	}
+	return list.Items, nil
+}
+
+// hasUserPDB returns true when an existing non-temporary PDB has the same
+// selector as the controller's pod selector. This is a conservative
+// equality check: a broader user PDB will NOT be detected, and we'll create
+// our own. Eviction will then respect the most restrictive of the two,
+// preserving the user's intent.
+func hasUserPDB(existing []policyv1.PodDisruptionBudget, controllerSelector *metav1.LabelSelector) bool {
+	if controllerSelector == nil {
+		return false
+	}
+	return slices.ContainsFunc(existing, func(pdb policyv1.PodDisruptionBudget) bool {
+		return !isTemporaryPDB(&pdb) && reflect.DeepEqual(pdb.Spec.Selector, controllerSelector)
+	})
+}
+
+func isTemporaryPDB(pdb *policyv1.PodDisruptionBudget) bool {
+	return pdb.Labels[pdbManagedByLabelKey] == pdbManagedByLabelValue &&
+		pdb.Labels[pdbTempLabelKey] == pdbTempLabelValue
+}
+
+// createTempPDB writes (or no-ops if our PDB already exists) a temporary
+// PodDisruptionBudget with maxUnavailable: 1. Existing PDBs that aren't ours
+// at the same name are left alone with a logged warning — that's a name
+// collision the user must resolve.
+func createTempPDB(ctx context.Context, ctrlClient client.Client, c controllerInfo, dryRun bool) error {
+	name := tempPDBName(c.Kind, c.Name)
+	if dryRun {
+		log.Printf("[dry-run] would create PDB %s/%s (maxUnavailable: 1, selector: %s)", c.Namespace, name, formatSelector(c.Selector))
+		return nil
+	}
+
+	existing := &policyv1.PodDisruptionBudget{}
+	err := ctrlClient.Get(ctx, client.ObjectKey{Namespace: c.Namespace, Name: name}, existing)
+	switch {
+	case err == nil:
+		if !isTemporaryPDB(existing) {
+			log.Printf("Warning: PDB %s/%s exists but is not labelled as temporary; leaving it untouched", c.Namespace, name)
+			return nil
+		}
+		// Our PDB from a previous (possibly crashed) run. Leave as-is; the
+		// cleanup step will remove it at the end of the current run.
+		return nil
+	case !apierrors.IsNotFound(err):
+		return fmt.Errorf("failed to get PDB %s/%s: %w", c.Namespace, name, err)
+	}
+
+	maxUnavailable := intstr.FromInt(1)
+	pdb := &policyv1.PodDisruptionBudget{
+		TypeMeta: metav1.TypeMeta{APIVersion: "policy/v1", Kind: "PodDisruptionBudget"},
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      name,
+			Namespace: c.Namespace,
+			Labels: map[string]string{
+				pdbManagedByLabelKey: pdbManagedByLabelValue,
+				pdbTempLabelKey:      pdbTempLabelValue,
+			},
+		},
+		Spec: policyv1.PodDisruptionBudgetSpec{
+			Selector:       c.Selector.DeepCopy(),
+			MaxUnavailable: &maxUnavailable,
+		},
+	}
+	if err := ctrlClient.Create(ctx, pdb); err != nil {
+		return fmt.Errorf("failed to create PDB %s/%s: %w", c.Namespace, name, err)
+	}
+	log.Printf("Created temporary PDB %s/%s for %s/%s (maxUnavailable: 1).", c.Namespace, name, c.Kind, c.Name)
+	return nil
+}
+
+// tempPDBName builds a DNS-label-safe PDB name. Long controller names are
+// truncated so the final name (including the suffix) fits the 63-char limit.
+func tempPDBName(kind, controllerName string) string {
+	prefix := strings.ToLower(kind) + "-" + controllerName
+	if len(prefix)+len(pdbNameSuffix) > validation.DNS1123LabelMaxLength {
+		prefix = prefix[:validation.DNS1123LabelMaxLength-len(pdbNameSuffix)]
+	}
+	return prefix + pdbNameSuffix
+}
+
+func formatSelector(s *metav1.LabelSelector) string {
+	if s == nil {
+		return "<nil>"
+	}
+	parts := lo.MapToSlice(s.MatchLabels, func(k, v string) string {
+		return k + "=" + v
+	})
+	return strings.Join(parts, ",")
 }