Expose PodAffinity and PodAntiAffinity struct and build overrides

This patch introduces a very basic struct to expose Pod Affinity/Antiaffinity
and NodeAffinity interfaces as part of the Topology CR spec and it allows to
patch the (opinionated) default that is currently applied to the services
through DistributePods function call.

Signed-off-by: Francesco Pantano <[email protected]>

Author: fmount

modules/common/affinity/affinity.go

@@ -17,8 +17,12 @@ limitations under the License.
 package affinity
 
 import (
+	"encoding/json"
+	"fmt"
 	corev1 "k8s.io/api/core/v1"
+	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/strategicpatch"
 )
 
 // DistributePods - returns rule to ensure that two replicas of the same selector
@@ -27,8 +31,9 @@ func DistributePods(
 	selectorKey string,
 	selectorValues []string,
 	topologyKey string,
-) *corev1.Affinity {
-	return &corev1.Affinity{
+	overrides *OverrideSpec,
+) (*corev1.Affinity, error) {
+	defaultAffinity := &corev1.Affinity{
 		PodAntiAffinity: &corev1.PodAntiAffinity{
 			// This rule ensures that two replicas of the same selector
 			// should not run if possible on the same worker node
@@ -53,4 +58,46 @@ func DistributePods(
 			},
 		},
 	}
+	// patch the default affinity Object with the data passed as input
+	if overrides != nil {
+		patchedAffinity, err := toCoreAffinity(defaultAffinity, overrides)
+		return patchedAffinity, err
+	}
+	return defaultAffinity, nil
+}
+
+func toCoreAffinity(
+	affinity *v1.Affinity,
+	override *OverrideSpec,
+) (*v1.Affinity, error) {
+
+	aff := &v1.Affinity{
+		PodAntiAffinity: affinity.PodAntiAffinity,
+		PodAffinity:     affinity.PodAffinity,
+	}
+	if override != nil {
+		if override != nil {
+			origAffinit, err := json.Marshal(affinity)
+			if err != nil {
+				return aff, fmt.Errorf("error marshalling Affinity Spec: %w", err)
+			}
+			patch, err := json.Marshal(override)
+			if err != nil {
+				return aff, fmt.Errorf("error marshalling Affinity Spec: %w", err)
+			}
+
+			patchedJSON, err := strategicpatch.StrategicMergePatch(origAffinit, patch, v1.Affinity{})
+			if err != nil {
+				return aff, fmt.Errorf("error patching Affinity Spec: %w", err)
+			}
+
+			patchedSpec := v1.Affinity{}
+			err = json.Unmarshal(patchedJSON, &patchedSpec)
+			if err != nil {
+				return aff, fmt.Errorf("error unmarshalling patched Service Spec: %w", err)
+			}
+			aff = &patchedSpec
+		}
+	}
+	return aff, nil
 }

modules/common/affinity/affinity_test.go

@@ -47,13 +47,82 @@ var affinityObj = &corev1.Affinity{
 	},
 }
 
+// weightedPodAffinityTermOverride represents an Override passed to the Affinity
+// tests
+var weightedPodAffinityTermOverride = []corev1.WeightedPodAffinityTerm{
+	{
+		PodAffinityTerm: corev1.PodAffinityTerm{
+			LabelSelector: &metav1.LabelSelector{
+				MatchExpressions: []metav1.LabelSelectorRequirement{
+					{
+						Key:      "CustomKeySelector",
+						Operator: metav1.LabelSelectorOpIn,
+						Values: []string{
+							"selectorValue1",
+							"selectorValue2",
+							"selectorValue3",
+						},
+					},
+				},
+			},
+			TopologyKey: "CustomTopologyKey",
+		},
+		Weight: 80,
+	},
+}
+
 func TestDistributePods(t *testing.T) {
 
 	t.Run("Default pod distribution", func(t *testing.T) {
 		g := NewWithT(t)
+		d, _ := DistributePods("ThisSelector", []string{"selectorValue1", "selectorValue2"}, "ThisTopologyKey", nil)
+		g.Expect(d).To(BeEquivalentTo(affinityObj))
+	})
 
-		d := DistributePods("ThisSelector", []string{"selectorValue1", "selectorValue2"}, "ThisTopologyKey")
+	// Override the default AntiAffinity
+	t.Run("Pod distribution with overrides", func(t *testing.T) {
+		// The resulting affinity that should be assigned to the Pod
+		var expectedAffinity = &corev1.Affinity{
+			PodAffinity:  nil,
+			NodeAffinity: nil,
+			PodAntiAffinity: &corev1.PodAntiAffinity{
+				PreferredDuringSchedulingIgnoredDuringExecution: weightedPodAffinityTermOverride,
+			},
+		}
+		affinityOverride := &OverrideSpec{
+			PodAffinity: nil,
+			PodAntiAffinity: &corev1.PodAntiAffinity{
+				PreferredDuringSchedulingIgnoredDuringExecution: weightedPodAffinityTermOverride,
+			},
+			NodeAffinity: nil,
+		}
+		g := NewWithT(t)
+		d, _ := DistributePods("ThisSelector", []string{"selectorValue1", "selectorValue2"}, "ThisTopologyKey", affinityOverride)
+		g.Expect(d).To(BeEquivalentTo(expectedAffinity))
+	})
 
-		g.Expect(d).To(BeEquivalentTo(affinityObj))
+	// Override the Affinity but keep the default AntiAffinity
+	t.Run("Pod distribution with overrides", func(t *testing.T) {
+		// The resulting affinity that should be assigned to the Pod
+		var expectedAffinity = &corev1.Affinity{
+			// the default PodAntiAffinity defined in the DistributePods function
+			// is applied, while PodAffinity is the result of the override passed
+			// as input
+			PodAntiAffinity: affinityObj.PodAntiAffinity,
+			NodeAffinity:    nil,
+			PodAffinity: &corev1.PodAffinity{
+				PreferredDuringSchedulingIgnoredDuringExecution: weightedPodAffinityTermOverride,
+			},
+		}
+		affinityOverride := &OverrideSpec{
+			PodAntiAffinity: nil,
+			PodAffinity: &corev1.PodAffinity{
+				PreferredDuringSchedulingIgnoredDuringExecution: weightedPodAffinityTermOverride,
+			},
+			NodeAffinity: nil,
+		}
+		g := NewWithT(t)
+		d, _ := DistributePods("ThisSelector", []string{"selectorValue1", "selectorValue2"}, "ThisTopologyKey", affinityOverride)
+		g.Expect(d).To(BeEquivalentTo(expectedAffinity))
 	})
 }

modules/common/affinity/types.go

@@ -0,0 +1,36 @@
+/*
+Copyright 2024 Red Hat
+
+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.
+*/
+
+// +kubebuilder:object:generate:=true
+
+package affinity
+
+import (
+	corev1 "k8s.io/api/core/v1"
+)
+
+// OverrideSpec -
+type OverrideSpec struct {
+	// Describes pod affinity scheduling rules (e.g. co-locate this pod in the same node, zone, etc. as some other pod(s)).
+	// +optional
+	PodAffinity *corev1.PodAffinity `json:"podAffinity,omitempty" protobuf:"bytes,2,opt,name=podAffinity"`
+	// Describes pod anti-affinity scheduling rules (e.g. avoid putting this pod in the same node, zone, etc. as some other pod(s)).
+	// +optional
+	PodAntiAffinity *corev1.PodAntiAffinity `json:"podAntiAffinity,omitempty" protobuf:"bytes,3,opt,name=podAntiAffinity"`
+	// Describes node affinity scheduling rules for the pod.
+	// +optional
+	NodeAffinity *corev1.NodeAffinity `json:"nodeAffinity,omitempty" protobuf:"bytes,1,opt,name=nodeAffinity"`
+}