/**
  * Returns an array of servers NOT assigned to a cluster
  *
  * @param
  *
  * @return array
  */
 public function getAvailableServers()
 {
     $_assigned = [];
     $_rows = Server::get(['id', 'server_type_id', 'server_id_text']);
     $_response = ['web' => [], 'app' => [], 'db' => []];
     foreach (ClusterServer::get(['server_id']) as $_row) {
         $_assigned[] = $_row->server_id;
     }
     foreach ($_rows as $_row) {
         if (!in_array($_row->id, $_assigned)) {
             $_response[strtolower(ServerTypes::nameOf($_row->server_type_id, false))][] = ['id' => $_row->id, 'name' => $_row->server_id_text];
         }
     }
     return $_response;
 }