Add comma-separated list to dynamic config as well

Author: eberlep

controllers/postgres_controller.go

@@ -1137,7 +1137,14 @@ func (r *PostgresReconciler) checkAndUpdatePatroniReplicationConfig(log logr.Log
 			log.V(debugLogLevel).Info("create_replica_methods mismatch, updating and requeing", "response", resp)
 			return requeueAfterReconcile, r.httpPatchPatroni(log, ctx, instance, leaderIP, nil)
 		}
-		if resp.StandbyCluster.Host != instance.Spec.PostgresConnection.ConnectionIP {
+
+		// Force Patroni to add target_session_attrs=read-write by providing a comma separated list (with the same IP...).
+		// This hopefully prevents cascading replicating by preventing the standby leader pod of the standby cluster to
+		// connect to a read-only pod in the primary cluster (which would break our sync replication to the standby cluster).
+		// https://patroni.readthedocs.io/en/latest/standby_cluster.html
+		standbyHosts := strings.Join([]string{instance.Spec.PostgresConnection.ConnectionIP, instance.Spec.PostgresConnection.ConnectionIP}, ",")
+
+		if resp.StandbyCluster.Host != standbyHosts {
 			log.V(debugLogLevel).Info("host mismatch, updating and requeing", "updating", resp)
 			return requeueAfterReconcile, r.httpPatchPatroni(log, ctx, instance, leaderIP, nil)
 		}
@@ -1249,10 +1256,16 @@ func (r *PostgresReconciler) httpPatchPatroni(log logr.Logger, ctx context.Conte
 			request.SynchronousNodesAdditional = nil
 		}
 	} else {
+		// Force Patroni to add target_session_attrs=read-write by providing a comma separated list (with the same IP...).
+		// This hopefully prevents cascading replicating by preventing the standby leader pod of the standby cluster to
+		// connect to a read-only pod in the primary cluster (which would break our sync replication to the standby cluster).
+		// https://patroni.readthedocs.io/en/latest/standby_cluster.html
+		standbyHosts := strings.Join([]string{instance.Spec.PostgresConnection.ConnectionIP, instance.Spec.PostgresConnection.ConnectionIP}, ",")
+
 		request = PatroniConfig{
 			StandbyCluster: &PatroniStandbyCluster{
 				CreateReplicaMethods: []string{"basebackup_fast_xlog"},
-				Host:                 instance.Spec.PostgresConnection.ConnectionIP,
+				Host:                 standbyHosts,
 				Port:                 int(instance.Spec.PostgresConnection.ConnectionPort),
 				ApplicationName:      instance.ToPeripheralResourceName(),
 			},