Terraform lookup函数未默认返回null致Azure函数应用部署报错

尝试用Terraform的lookup函数根据输入指定Azure Web应用栈，执行terraform plan时触发参数冲突错误，提示application_stack块中仅能指定一个栈参数。预期java_version返回null（手动设置null时可正常运行），但当前lookup写法导致node_version与java_version同时被指定，需排查问题原因。

报错信息 #

terraform plan
╷
│ Error: Invalid combination of arguments
│
│   with azurerm_windows_function_app.example,
│   on functionapp.tf line 67, in resource "azurerm_windows_function_app" "example":
│   67:     application_stack {
│
│ "site_config.0.application_stack.0.powershell_core_version": only one of
│ `site_config.0.application_stack.0.dotnet_version,site_config.0.application_stack.0.java_version,site_config.0.application_stack.0.node_version,site_config.0.application_stack.0.powershell_core_version,site_config.0.application_stack.0.use_custom_runtime`
│ can be specified, but `site_config.0.application_stack.0.java_version,site_config.0.application_stack.0.node_version` were specified.

原Terraform代码 #

variable "applicationstack" {
  type = string
  default = "node"  
}

variable "stack_version" {
  type = map
  default ={
    node = "~14"
    java = "8"
  }
}

resource "azurerm_resource_group" "example" {
  name     = "eus-s-test-rg-01"
  location = "eastus"
}

resource "azurerm_storage_account" "example" {
  name                     = "eusperftestjs01"
  resource_group_name      = azurerm_resource_group.example.name
  location                 = azurerm_resource_group.example.location
  account_tier             = "Standard"
  account_replication_type = "LRS"
}


resource "azurerm_service_plan" "example" {
  name                = "example-app-service-plan"
  resource_group_name = azurerm_resource_group.example.name
  location            = azurerm_resource_group.example.location
  os_type             = "Windows"
  sku_name            = "Y1"
}

resource "azurerm_windows_function_app" "example" {
  name                = "eus-perf-test-js-01"
  resource_group_name = azurerm_resource_group.example.name
  location            = azurerm_resource_group.example.location
  storage_account_name       = azurerm_storage_account.example.name
  storage_account_access_key = azurerm_storage_account.example.primary_access_key
  service_plan_id            = azurerm_service_plan.example.id
  site_config {
    application_stack {
      node_version = lookup(var.stack_version,var.applicationstack,null)
      java_version = lookup(var.stack_version,var.applicationstack,null)
    }
  }
}

解决方案 #

问题核心不是lookup语法错误，而是你同时显式声明了node_version和java_version两个参数——哪怕它们的值是null，Terraform依然会将这两个参数传递给Azure资源，而Azure的函数应用资源不允许同时指定多个栈版本参数。

方法1：使用动态块（推荐，扩展性好） #

通过Terraform的动态块，仅生成对应栈类型的版本参数：

resource "azurerm_windows_function_app" "example" {
  name                = "eus-perf-test-js-01"
  resource_group_name = azurerm_resource_group.example.name
  location            = azurerm_resource_group.example.location
  storage_account_name       = azurerm_storage_account.example.name
  storage_account_access_key = azurerm_storage_account.example.primary_access_key
  service_plan_id            = azurerm_service_plan.example.id
  site_config {
    dynamic "application_stack" {
      for_each = [var.applicationstack]
      content {
        (application_stack.value)_version = lookup(var.stack_version, application_stack.value, null)
      }
    }
  }
}

• 动态块会根据var.applicationstack的值，仅生成对应栈的版本参数（比如指定node时，只会生成node_version = "~14"，不会出现java_version参数）
• 后续新增栈类型（如dotnet）时，只需在stack_version变量中添加对应值，无需修改资源配置

方法2：条件判断显式赋值 #

如果栈类型较少，也可以用条件判断单独控制每个参数的赋值：

resource "azurerm_windows_function_app" "example" {
  name                = "eus-perf-test-js-01"
  resource_group_name = azurerm_resource_group.example.name
  location            = azurerm_resource_group.example.location
  storage_account_name       = azurerm_storage_account.example.name
  storage_account_access_key = azurerm_storage_account.example.primary_access_key
  service_plan_id            = azurerm_service_plan.example.id
  site_config {
    application_stack {
      node_version = var.applicationstack == "node" ? lookup(var.stack_version, "node", null) : null
      java_version = var.applicationstack == "java" ? lookup(var.stack_version, "java", null) : null
    }
  }
}

这种方式需要为每个栈类型单独写条件判断，适合栈类型固定的场景。

内容的提问来源于stack exchange，提问作者Uday Kiran