tensorflow::ServerDef ReplaceTaskInServerDef(
    const tensorflow::ServerDef& server_def, int task_index) {
  tensorflow::ServerDef server_def_copy = server_def;
  tensorflow::ClusterDef* cluster_def = server_def_copy.mutable_cluster();
  tensorflow::JobDef* job_def = cluster_def->mutable_job(0);
  const int port = tensorflow::testing::PickUnusedPortOrDie();
  job_def->mutable_tasks()->at(task_index) =
      tensorflow::strings::StrCat("localhost:", port);