我想知道是否有可能从模块输出中选择一个特定的属性，因为我知道我调用模块时使用的是循环。
1.在Map上使用for_each调用backup_policy模块
1.将创建策略并在模块输出中提供其ID
1.调用VM模块并在调用中指定VM必须与之链接的策略ID
下面是代码示例：
调用backup_policy模块：

locals {
  backup_policies = {
    "daily-critical" = {
    ...
    }
    "daily-qa" = {
    ...
    }
  }
}

module "backup_policy" {
  source = "path/to/my/module"

  for_each = local.backup_policies

  location            = local.location
  resource_group_name = module.rg.resource_group_name

  vm_backup_policy_name = "${each.key}-backup-policy"
}

备份策略模块代码：

resource "azurerm_backup_policy_vm" "vm_backup_policy" {
  name                = var.vm_backup_policy_name
  resource_group_name = var.resource_group_name
  recovery_vault_name = var.recovery_vault_name
  ....
  }

backup_policy模块输出代码：

output "vm_backup_policy_id" {
  value       = azurerm_backup_policy_vm.vm_backup_policy.id
}

现在我的策略已经创建好了，我想使用策略ID将它们链接到虚拟机。但是我想使用策略名称指定哪个策略必须链接到哪个虚拟机。大致如下所示（请看最后一行）：

locals {
  location = "East US"

  vms = {
    "my-vm1" = {
      size          = "Standard_DS12_v2"
      backup_policy = "daily-critical"
    }
    "my-vm2" = {
      size          = "Standard_DS12_v2"
      backup_policy = "daily-qa"
    }
  }
}

module "vms" {
  source = "path/to/my/module"

  for_each            = local.vms
  vm_name             = each.key
  location            = local.location
  resource_group_name = module.rg.resource_group_name

  backup_policy_id = module.backup_policy.vm_backup_policy_id[each.value["backup_policy"]]
}

是否可以或者必须向backup_policy模块发送一个名称列表，并在模块端执行for_each，以便在输出中生成Map？