code: def _client_builder(self):
          
          client_config = self.app.config.get('SEARCH_CLIENT_CONFIG') or {}
          client_config.setdefault(
              'hosts', self.app.config.get('SEARCH_ELASTIC_HOSTS'))
          client_config.setdefault('connection_class', RequestsHttpConnection)
          return Elasticsearch(**client_config)
docs: Build Elasticsearch client.