code: func (b *Builder) KeyNodes(key int) []*BuilderNode {
  	nodes := make([]*BuilderNode, 0, len(b.ring.ReplicaToPartitionToNode))
  	partition := key % len(b.ring.ReplicaToPartitionToNode[0])
  	for _, partitionToNode := range b.ring.ReplicaToPartitionToNode {
  		nodes = append(nodes, b.nodes[partitionToNode[partition]])
  	}
  	return nodes
  }
docs: // KeyNodes returns the nodes responsible for the key given. There will be on
  // node for each replica; in other words:
  // len(b.KeyNodes(k)) == b.ReplicaCount().