Check whether pod matches the inter-pod anti-affinity of another Pod in a given Node in NodeFit() (#1356)

* Check if Pod matches inter-pod anti-affinity of other pod on node as part of NodeFit()

* Add unit tests for checking inter-pod anti-affinity match in NodeFit()
* Export setPodAntiAffinity() helper func to test utils

* Add docs for inter-pod anti-affinity in README

* Refactor logic for inter-pod anti-affinity to use in multiple pkgs
* Move logic for finding match between pods with antiaffinity out of framework to reuse in other pkgs
* Move interpod antiaffinity funcs to pkg/utils/predicates.go

* Add unit tests for inter-pod anti-affinity check
* Test logic in GroupByNodeName
* Test NodeFit() case where pods matches inter-pod anti-affinity
* Test for inter-pod anti-affinity pods  match terms, have label selector

* NodeFit inter-pod anti-affinity check returns early if affinity spec not set

pkg/utils/predicates.go

@@ -22,6 +22,7 @@ import (
 	"sort"
 
 	v1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/component-helpers/scheduling/corev1"
 	"k8s.io/klog/v2"
@@ -299,3 +300,84 @@ func GetNodeWeightGivenPodPreferredAffinity(pod *v1.Pod, node *v1.Node) (int32,
 	}
 	return sumWeights, nil
 }
+
+func CreateNodeMap(nodes []*v1.Node) map[string]*v1.Node {
+	m := make(map[string]*v1.Node, len(nodes))
+	for _, node := range nodes {
+		m[node.GetName()] = node
+	}
+	return m
+}
+
+// CheckPodsWithAntiAffinityExist checks if there are other pods on the node that the current pod cannot tolerate.
+func CheckPodsWithAntiAffinityExist(pod *v1.Pod, pods map[string][]*v1.Pod, nodeMap map[string]*v1.Node) bool {
+	affinity := pod.Spec.Affinity
+	if affinity != nil && affinity.PodAntiAffinity != nil {
+		for _, term := range getPodAntiAffinityTerms(affinity.PodAntiAffinity) {
+			namespaces := getNamespacesFromPodAffinityTerm(pod, &term)
+			selector, err := metav1.LabelSelectorAsSelector(term.LabelSelector)
+			if err != nil {
+				klog.ErrorS(err, "Unable to convert LabelSelector into Selector")
+				return false
+			}
+			for namespace := range namespaces {
+				for _, existingPod := range pods[namespace] {
+					if existingPod.Name != pod.Name && podMatchesTermsNamespaceAndSelector(existingPod, namespaces, selector) {
+						node, ok := nodeMap[pod.Spec.NodeName]
+						if !ok {
+							continue
+						}
+						nodeHavingExistingPod, ok := nodeMap[existingPod.Spec.NodeName]
+						if !ok {
+							continue
+						}
+						if hasSameLabelValue(node, nodeHavingExistingPod, term.TopologyKey) {
+							klog.V(1).InfoS("Found Pods matching PodAntiAffinity", "pod with anti-affinity", klog.KObj(pod))
+							return true
+						}
+					}
+				}
+			}
+		}
+	}
+	return false
+}
+
+// getPodAntiAffinityTerms gets the antiaffinity terms for the given pod.
+func getPodAntiAffinityTerms(podAntiAffinity *v1.PodAntiAffinity) (terms []v1.PodAffinityTerm) {
+	if podAntiAffinity != nil {
+		if len(podAntiAffinity.RequiredDuringSchedulingIgnoredDuringExecution) != 0 {
+			terms = podAntiAffinity.RequiredDuringSchedulingIgnoredDuringExecution
+		}
+	}
+	return terms
+}
+
+// hasSameLabelValue checks if the pods are in the same topology zone.
+func hasSameLabelValue(node1, node2 *v1.Node, key string) bool {
+	if node1.Name == node2.Name {
+		return true
+	}
+
+	// no match if node has empty labels
+	node1Labels := node1.Labels
+	if node1Labels == nil {
+		return false
+	}
+	node2Labels := node2.Labels
+	if node2Labels == nil {
+		return false
+	}
+
+	// no match if node has no topology zone label with given key
+	value1, ok := node1Labels[key]
+	if !ok {
+		return false
+	}
+	value2, ok := node2Labels[key]
+	if !ok {
+		return false
+	}
+
+	return value1 == value2
+}

pkg/utils/predicates_test.go

@@ -6,6 +6,7 @@ import (
 
 	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"sigs.k8s.io/descheduler/test"
 )
 
 func TestUniqueSortTolerations(t *testing.T) {
@@ -1041,3 +1042,71 @@ func TestPodNodeAffinityWeight(t *testing.T) {
 		})
 	}
 }
+
+func TestCheckPodsWithAntiAffinityExist(t *testing.T) {
+	tests := []struct {
+		name            string
+		pod             *v1.Pod
+		podsInNamespace map[string][]*v1.Pod
+		nodeMap         map[string]*v1.Node
+		affinity        *v1.PodAntiAffinity
+		expMatch        bool
+	}{
+		{
+			name: "found pod matching pod anti-affinity",
+			pod:  test.PodWithPodAntiAffinity(test.BuildTestPod("p1", 1000, 1000, "node", nil), "foo", "bar"),
+			podsInNamespace: map[string][]*v1.Pod{
+				"default": {
+					test.PodWithPodAntiAffinity(test.BuildTestPod("p2", 1000, 1000, "node", nil), "foo", "bar"),
+				},
+			},
+			nodeMap: map[string]*v1.Node{
+				"node": test.BuildTestNode("node", 64000, 128*1000*1000*1000, 2, func(node *v1.Node) {
+					node.ObjectMeta.Labels = map[string]string{
+						"region": "main-region",
+					}
+				}),
+			},
+			expMatch: true,
+		},
+		{
+			name: "no match with invalid label selector",
+			pod: &v1.Pod{
+				Spec: v1.PodSpec{
+					Affinity: &v1.Affinity{
+						PodAntiAffinity: &v1.PodAntiAffinity{
+							RequiredDuringSchedulingIgnoredDuringExecution: []v1.PodAffinityTerm{
+								{
+									LabelSelector: &metav1.LabelSelector{
+										MatchLabels: map[string]string{
+											"wrong": "selector",
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			podsInNamespace: map[string][]*v1.Pod{},
+			nodeMap:         map[string]*v1.Node{},
+			expMatch:        false,
+		},
+		{
+			name: "no match if pod does not match terms namespace",
+			pod: test.PodWithPodAntiAffinity(test.BuildTestPod("p1", 1000, 1000, "node", func(pod *v1.Pod) {
+				pod.Namespace = "other"
+			}), "foo", "bar"),
+			podsInNamespace: map[string][]*v1.Pod{},
+			nodeMap:         map[string]*v1.Node{},
+			expMatch:        false,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if match := CheckPodsWithAntiAffinityExist(test.pod, test.podsInNamespace, test.nodeMap); match != test.expMatch {
+				t.Errorf("exp %v got %v", test.expMatch, match)
+			}
+		})
+	}
+}

pkg/utils/priority.go

@@ -14,10 +14,10 @@ import (
 
 const SystemCriticalPriority = 2 * int32(1000000000)
 
-// GetNamespacesFromPodAffinityTerm returns a set of names
+// getNamespacesFromPodAffinityTerm returns a set of names
 // according to the namespaces indicated in podAffinityTerm.
 // If namespaces is empty it considers the given pod's namespace.
-func GetNamespacesFromPodAffinityTerm(pod *v1.Pod, podAffinityTerm *v1.PodAffinityTerm) sets.Set[string] {
+func getNamespacesFromPodAffinityTerm(pod *v1.Pod, podAffinityTerm *v1.PodAffinityTerm) sets.Set[string] {
 	names := sets.New[string]()
 	if len(podAffinityTerm.Namespaces) == 0 {
 		names.Insert(pod.Namespace)
@@ -27,9 +27,9 @@ func GetNamespacesFromPodAffinityTerm(pod *v1.Pod, podAffinityTerm *v1.PodAffini
 	return names
 }
 
-// PodMatchesTermsNamespaceAndSelector returns true if the given <pod>
+// podMatchesTermsNamespaceAndSelector returns true if the given <pod>
 // matches the namespace and selector defined by <affinityPod>`s <term>.
-func PodMatchesTermsNamespaceAndSelector(pod *v1.Pod, namespaces sets.Set[string], selector labels.Selector) bool {
+func podMatchesTermsNamespaceAndSelector(pod *v1.Pod, namespaces sets.Set[string], selector labels.Selector) bool {
 	if !namespaces.Has(pod.Namespace) {
 		return false
 	}