code: def peer_retrieve(key, relation_name='cluster'):
      
      cluster_rels = relation_ids(relation_name)
      if len(cluster_rels) > 0:
          cluster_rid = cluster_rels[0]
          return relation_get(attribute=key, rid=cluster_rid,
                              unit=local_unit())
      else:
          raise ValueError('Unable to detect'
                           'peer relation {}'.format(relation_name))
docs: Retrieve a named key from peer relation `relation_name`.