Terraform模块创建Azure子网后无法获取资源ID的问题

报错信息 #

Error: Unsupported attribute
│
│   on outputs.tf line 3, in output "one_azure_subnet_id":
│    3:     for id in keys(var.subnets) : id => module.Subnet.azure_subnet_id[id]
│     ├────────────────
│     │ module.Subnet is object with 3 attributes
│
│ This object does not have an attribute named "azure_subnet_id".

场景说明 #

通过自定义Terraform子网模块批量创建3个子网后，在主项目的输出配置中尝试获取所有子网ID时触发上述错误。

子网模块结构 #

Subnet/
┣ main.tf
┣ outputs.tf
┗ variables.tf

子网模块代码 #

main.tf

resource "azurerm_subnet" "subnet_module" {
  name                 = var.subnet_name
  resource_group_name  = var.resource_group_name
  virtual_network_name = var.vnet_name
  address_prefixes     = var.address_prefixes
}

outputs.tf

output "azure_subnet_id" {
  value = azurerm_subnet.subnet_module[*].id
  description = "Lists the ID's of the subnets"
}

variables.tf

variable "subnet_name" {
  type = string
}

variable "address_prefixes" {
  type = list(string)
}

variable "resource_group_name" {
  type        = string
  description = "Resource Group Name"
}

variable "vnet_name" {
  type = string
  description = "vnet name"
}

主项目代码 #

模块调用配置 #

module "Subnet" {
  source               = "./Modules/Subnet"
  for_each             = var.subnets
  subnet_name          = each.value["name"]
  address_prefixes     = each.value["address_prefixes"]
  resource_group_name  = data.azurerm_resource_group.rg.name
  vnet_name = azurerm_virtual_network.vnet.name
}

子网变量定义 #

subnets = {
  subnet_1 = {
    name             = "dev-virtual-subnet"
    address_prefixes = ["10.13.1.0/24"]
  }
  subnet_2 = {
    name             = "test-virtual-subnet"
    address_prefixes = ["10.13.2.0/24"]
  }
  subnet_3 = {
    name             = "staging-virtual-subnet"
    address_prefixes = ["10.13.3.0/24"]
  }
}

出错的输出配置 #

output "onefms_azure_subnet_id" {
  value = {
    for id in keys(var.subnets) : id => module.Subnet.azure_subnet_id[id]
  }
  description = "Lists the ID's of the subnets"
}

错误原因及修复方案 #

错误原因 #

1. 使用for_each调用模块时，module.Subnet会变成以for_each键为索引的映射对象，而非单个模块实例。直接访问module.Subnet.azure_subnet_id会报错，因为映射对象本身没有该属性，属性属于每个子模块实例。
2. 子网模块的输出使用[*]展开，但该模块每次仅创建单个子网，azurerm_subnet.subnet_module是单个资源而非列表，[*]会生成冗余的单元素列表。

修复步骤 #

1. 调整子网模块的outputs.tf：
   移除不必要的[*]，直接输出单个子网ID：

   output "azure_subnet_id" {
     value = azurerm_subnet.subnet_module.id
     description = "The ID of the subnet"
   }
   

2. 修改主项目的outputs.tf：
   遍历module.Subnet映射，直接获取每个实例的输出值：

   output "onefms_azure_subnet_id" {
     value = {
       for k, subnet_module in module.Subnet : k => subnet_module.azure_subnet_id
     }
     description = "Lists the ID's of the subnets"
   }
   

修改后即可正常生成以subnet_1/subnet_2/subnet_3为键、对应子网ID为值的映射输出。

内容的提问来源于stack exchange，提问作者Jason