improve docs

docs/administrator.md

@@ -154,6 +154,20 @@ data:
   pod_antiaffinity_topology_key: "failure-domain.beta.kubernetes.io/zone"
 ```
 
+### Pod Disruption Budget
+
+By default the operator uses a PodDisruptionBudget (PDB) to protect the cluster
+from voluntarily disruptions and hence unwanted DB downtime. The `MinAvailable`
+parameter of the PDB is set to `1` which makes it work for single-node clusters
+or in situations when there is no master (e.g. standby clusters).
+
+The PDB is only relaxed in two scenarios:
+* If a cluster is scaled down to `0` instances (e.g. for draining nodes)
+* If the PDB is disabled in the configuration (`enable_pod_disruption_budget`)
+
+The PDB is still in place having `MinAvailable` set to `0`. If enabled it will
+be automatically set to `1` on scale up.
+
 ### Add cluster-specific labels
 
 In some cases, you might want to add `labels` that are specific to a given

docs/reference/operator_parameters.md

@@ -162,10 +162,11 @@ configuration they are grouped under the `kubernetes` key.
   the template.
 
 * **enable_pod_disruption_budget**
-  if disabled `MinAvailable` in the PDB's spec will be set to `0`. That means
-  the PDB will get created anyway. The PDB is also relaxed when scaling down the
-  Postgres cluster to `"numberOfInstances": 0`. By default PDB is enabled which
-  results in `"MinAvailable": 1`.
+  PDB is enabled by default to protect the cluster from voluntarily disruptions
+  and hence unwanted DB downtime. However, on some cloud providers it could be
+  necessary to temporarily disabled it, e.g. for node updates. See
+  [admin docs](../administrator.md#pod-disruption-budget) for more information.
+  Default is true.
 
 * **secret_name_template**
   a template for the name of the database user secrets generated by the