Terraform-调用模块抛出错误时引用实例值

resource "azurerm_subnet" "subnet" {
  count                     = "${length(var.subnet_names)}"
  name                      = "${element(var.subnet_names, count.index)}"
  resource_group_name       = "${var.vnet_rg_name}"
  virtual_network_name      = "${data.azurerm_virtual_network.vnet.name}"
  address_prefix            = "${element(var.subnet_prefixes, count.index)}"
  service_endpoints         = ["Microsoft.Sql","Microsoft.Storage","Microsoft.AzureCosmosDB"]
  network_security_group_id = "${data.azurerm_network_security_group.required_nsg.id}"
  route_table_id            = "${element(azurerm_route_table.routetable.*.id, count.index)}"
  depends_on                = ["azurerm_route_table.routetable"]
}

然后,我尝试使用模块创建一些路由,但当我尝试使用来自特定模块实例的属性为变量传递值时 azurerm_subnet.subnet 资源,它抛出错误:

module "insidedmzroutes" {
  source           = "./modules/dmzroutes"
  subnet_name      = "${azurerm_subnet.subnet.5.name}"
  vnet_rg          = "${data.azurerm_resource_group.vnet_rg.name}"
  route_table_name = "${azurerm_route_table.routetable.5.name}"
  next_hop_ip      = "${cidrhost(azurerm_subnet.subnet.5.address_prefix, 4)}"
  subnet_names     = ["${var.subnet_names}"]
  subnet_prefixes  = ["${var.subnet_prefixes}"]
}

这不起作用,或者我的引用构造不正确吗?