code: def peer_store(key, value, relation_name='cluster'):
      
      cluster_rels = relation_ids(relation_name)
      if len(cluster_rels) > 0:
          cluster_rid = cluster_rels[0]
          relation_set(relation_id=cluster_rid,
                       relation_settings={key: value})
      else:
          raise ValueError('Unable to detect '
                           'peer relation {}'.format(relation_name))
docs: Store the key/value pair on the named peer relation `relation_name`.