Terraform中不为所有子网关联路由表的报错解决咨询

当使用Terraform批量创建虚拟网络及子网时，若部分子网无需关联路由表（如示例中的subnet2），直接省略route_table配置会触发azurerm_subnet_route_table_association资源的必填参数错误，报错信息如下：

│ Missing required argument
│
│ with module.virtual_network["test-vnet"].azurerm_subnet_route_table_association.route-link-subnet["subnet2"],
│ on modules\virtualNetwork\main.tf line 30, in resource "azurerm_subnet_route_table_association" "route-link-subnet":
│ 30: route_table_id = each.value.route_table
│
│ The argument "route_table_id" is required, but no definition was found. 

现有配置信息 #

变量定义

variable "networks" {
  type = map(object({
    resource_group_name = string
    location            = string
    addressSpace        = list(string)
    dnsServers          = optional(list(string))
    subnets = map(object({
      addressPrefix                     = string
      privateEndpointNetworkPolicies    = optional(bool)
      privateLinkServiceNetworkPolicies = optional(bool)
      service_endpoints                 = optional(list(string))
      route_table                       = optional(string)
    }))
  }))
}

配置示例

networks = {
  test-vnet = {
    resource_group_name = "testrg"
    location            = "eastus"
    addressSpace        = ["10.229.192.0/20"]
    dnsServers          = ["10.231.18.4"]
    subnets = {
      subnet1 = {
        addressPrefix = "10.229.199.0/24"
        networkSecurityGroups = {
          subnet1-nsg = {
            security_rules = []
          }
        }
        route_table = "/subscriptions//resourceGroups/test-rg/providers/Microsoft.Network/routeTables/test-rt"
      }
      subnet2 = {
        addressPrefix                     = "10.229.198.0/24"
        privateEndpointNetworkPolicies    = true
        privateLinkServiceNetworkPolicies = true
        service_endpoints = [
          "Microsoft.Storage"
        ]
        networkSecurityGroups = {
          subnet2-nsg = {
            security_rules = []
          }
        }
      }
    }
  }
}

资源配置（原错误版本）

resource "azurerm_subnet_route_table_association" "route-link-subnet" {
  for_each       = var.subnets
  subnet_id      = module.subnets[each.key].subnet_id
  route_table_id = each.value.route_table
  depends_on = [
    module.subnets,
    azurerm_virtual_network.Virtual_Network
  ]
}

解决方案 #

核心思路是只对存在route_table配置的子网创建路由表关联资源，通过修改for_each的迭代范围，过滤掉未配置route_table的子网：

修改后的azurerm_subnet_route_table_association资源配置如下：

resource "azurerm_subnet_route_table_association" "route-link-subnet" {
  # 仅迭代包含route_table配置的子网
  for_each       = { for k, v in var.subnets : k => v if v.route_table != null }
  subnet_id      = module.subnets[each.key].subnet_id
  route_table_id = each.value.route_table
  depends_on = [
    module.subnets,
    azurerm_virtual_network.Virtual_Network
  ]
}

这样配置后，Terraform只会为指定了route_table的子网（如subnet1）创建路由表关联资源，未指定的子网（如subnet2）会跳过该资源的创建，避免必填参数错误。

内容的提问来源于stack exchange，提问作者Mr.cool