Add Pod Anti Affinity (#489)

* Add Pod Anti Affinity

pkg/cluster/k8sres.go

@@ -290,6 +290,26 @@ func nodeAffinity(nodeReadinessLabel map[string]string) *v1.Affinity {
 	}
 }
 
+func generatePodAffinity(labels labels.Set, topologyKey string, nodeAffinity *v1.Affinity) *v1.Affinity {
+	// generate pod anti-affinity to avoid multiple pods of the same Postgres cluster in the same topology , e.g. node
+	podAffinity := v1.Affinity{
+		PodAntiAffinity: &v1.PodAntiAffinity{
+			RequiredDuringSchedulingIgnoredDuringExecution: []v1.PodAffinityTerm{{
+				LabelSelector: &metav1.LabelSelector{
+					MatchLabels: labels,
+				},
+				TopologyKey: topologyKey,
+			}},
+		},
+	}
+
+	if nodeAffinity != nil && nodeAffinity.NodeAffinity != nil {
+		podAffinity.NodeAffinity = nodeAffinity.NodeAffinity
+	}
+
+	return &podAffinity
+}
+
 func tolerations(tolerationsSpec *[]v1.Toleration, podToleration map[string]string) []v1.Toleration {
 	// allow to override tolerations by postgresql manifest
 	if len(*tolerationsSpec) > 0 {
@@ -419,6 +439,8 @@ func generatePodTemplate(
 	kubeIAMRole string,
 	priorityClassName string,
 	shmVolume bool,
+	podAntiAffinity bool,
+	podAntiAffinityTopologyKey string,
 ) (*v1.PodTemplateSpec, error) {
 
 	terminateGracePeriodSeconds := terminateGracePeriod
@@ -437,7 +459,9 @@ func generatePodTemplate(
 		addShmVolume(&podSpec)
 	}
 
-	if nodeAffinity != nil {
+	if podAntiAffinity {
+		podSpec.Affinity = generatePodAffinity(labels, podAntiAffinityTopologyKey, nodeAffinity)
+	} else if nodeAffinity != nil {
 		podSpec.Affinity = nodeAffinity
 	}
 
@@ -813,7 +837,9 @@ func (c *Cluster) generateStatefulSet(spec *acidv1.PostgresSpec) (*v1beta1.State
 		c.OpConfig.PodServiceAccountName,
 		c.OpConfig.KubeIAMRole,
 		effectivePodPriorityClassName,
-		mountShmVolumeNeeded(c.OpConfig, spec)); err != nil {
+		mountShmVolumeNeeded(c.OpConfig, spec),
+		c.OpConfig.EnablePodAntiAffinity,
+		c.OpConfig.PodAntiAffinityTopologyKey); err != nil {
 		return nil, fmt.Errorf("could not generate pod template: %v", err)
 	}