NodeDefBuilder builder(absl::StrCat(xla_cluster_name, "_key_placeholder"),
                         "Placeholder");
  builder.Attr("dtype", DT_STRING);
  builder.Attr("shape", PartialTensorShape({2}));
  builder.Attr("_host_compute_call_node", xla_cluster_name);
  Status s = builder.Finalize(&key_def);
  if (!s.ok()) return s;

  Node* n = g->AddNode(key_def, &s);
  if (!s.ok()) return s;
  return n;
}

                           "Placeholder", opts.op_registry());
  TensorShapeProto shape;
  shape.add_dim()->set_size(2);
  return opts.WithAttr("shape", shape)
      .WithAttr("dtype", DT_STRING)
      .WithAttr("_host_compute_call_node", call_node)
      .FinalizeBuilder(&node_builder);
}

Node* RecvAtHost(ops::NodeOut key_input, const string& cluster,
                 const string& new_func_name, const string& oc_cluster,