<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _yarn_cluster_metrics(self, rm_address, instance, addl_tags):
 """ Get metrics related to YARN cluster """

        metrics_json = self._rest_request_to_json(rm_address, instance, YARN_CLUSTER_METRICS_PATH, addl_tags)

        if metrics_json:

            yarn_metrics = metrics_json[YARN_CLUSTER_METRICS_ELEMENT]

            if yarn_metrics is not None:
                self._set_yarn_metrics_from_json(addl_tags, yarn_metrics, YARN_CLUSTER_METRICS)