Changed comment and added documentation as requested

docs/administrator.md

@@ -146,6 +146,36 @@ data:
   ...
 ```
 
+### Enable pod anti affinity
+
+To ensure Postgres pods are running on different topologies, you can use [pod anti affinity](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/)
+and configure the required topology in the operator ConfigMap.
+
+Enable pod anti affinity by adding following line to the operator ConfigMap:
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: postgres-operator
+data:
+  enable_pod_antiaffinity: "true"
+```
+
+By default the topology key for the pod anti affinity is set to `kubernetes.io/hostname`,
+you can set another topology key e.g. `failure-domain.beta.kubernetes.io/zone` by adding following line
+to the operator ConfigMap, see [built-in node labels](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#interlude-built-in-node-labels) for available topology keys:
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: postgres-operator
+data:
+  enable_pod_antiaffinity: "true"
+  pod_antiaffinity_topology_key: "failure-domain.beta.kubernetes.io/zone"
+```
+
 ### Add cluster-specific labels
 
 In some cases, you might want to add `labels` that are specific to a given

docs/reference/operator_parameters.md

@@ -213,6 +213,14 @@ configuration they are grouped under the `kubernetes` key.
   that should be assigned to the Postgres pods. The priority class itself must be defined in advance.
   Default is empty (use the default priority class).
 
+* **enable_pod_antiaffinity**
+  toggles [pod anti affinity](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/) on the Postgres pods, to avoid multiple pods
+  of the same Postgres cluster in the same topology , e.g. node. The default is `false`.
+
+* **pod_antiaffinity_topology_key**
+  override
+  [topology key](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#interlude-built-in-node-labels)
+  for pod anti affinity. The default is `kubernetes.io/hostname`.
 
 ## Kubernetes resource requests
 

pkg/cluster/k8sres.go

@@ -291,7 +291,7 @@ 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 on instances on the same node
+	// 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{{