code: def sharded_cluster_link(rel, cluster_id=None,
                           shard_id=None, router_id=None, self_rel=False):
      
      clusters_href = '/v1/sharded_clusters'
      link = _SHARDED_CLUSTER_LINKS[rel].copy()
      link['href'] = link['href'].format(**locals())
      link['rel'] = 'self' if self_rel else rel
      return link
docs: Helper for getting a ShardedCluster link document, given a rel.