我试着用下面的代码来检查现有的资源

data "azurerm_virtual_network" "existing_vnet" {
  name                = "myVnet"
  resource_group_name = data.azurerm_resource_group.example.name
}

locals {
  vnet_exists = length(data.azurerm_virtual_network.existing_vnet) > 0
}

output "vnetcout" {
  value = local.vnet_exists
}

如果资源不存在，则会显示错误“resource not found”。

对于此外部数据源，可以使用：外部的|数据源|哈希公司/外部|Terraform Registry不检查预先存在的资源。
这里几乎可以使用任何编程语言。一个这样的例子，我试图创建VM，如果它不存在。

data "external" "vm_exists" {
      program = ["Powershell.exe", "C:\\Users\\xx\\checkexistence.ps1"]
    }

 output "vmexistsornot" {
      value = "${data.external.vm_exists.result.value}"
    }

**PowerShell代码：**Checkexistence.ps1

$rgName = "myrg"
    $vmName = "excpectedm"
    $vmExists = Get-AzVM -Name $vmName -ResourceGroupName $rgName -ErrorAction SilentlyContinue  
   # $vmexistsmsg="VM exists"
   # $vmnotexistsmsg="VM does not exist"
    if (!$vmExists) {
    Write-Output '{"value" :  "true" }'   
    } else {
    Write-Output '{"value" :  "false" }'
      
    }

最初只检查不存在：它必须返回true。

如果VM不存在，它将被创建。

resource "azurerm_network_interface" "example" {
  name                = "kaexample-nic"
 location            = data.azurerm_resource_group.example.location
  resource_group_name = data.azurerm_resource_group.example.name
  ip_configuration {
    name                          = "example-ip-config"
    subnet_id                     = azurerm_subnet.example.id
    private_ip_address_allocation = "Dynamic"
  }
}

resource "azurerm_virtual_network" "example" {
  name                = "kaexample-virtual-network"
  address_space       = ["10.0.0.0/16"]
  location            = data.azurerm_resource_group.example.location
  resource_group_name = data.azurerm_resource_group.example.name
}

resource "azurerm_subnet" "example" {
  name                 = "kkexample-subnet"
  address_prefixes     = ["10.0.0.0/24"]
  virtual_network_name = azurerm_virtual_network.example.name
  resource_group_name  = data.azurerm_resource_group.example.name
}

resource "azurerm_virtual_machine" "new_vm" {
  count = data.external.vm_exists.result.value == "true" ? 1 : 0

  name                = var.vm_name
  resource_group_name = var.resource_group_name
  location            = "eastus"
   vm_size               = "Standard_D4as_v5"
   network_interface_ids =  [azurerm_network_interface.example.id]

  

  storage_os_disk {
    name               = "my_os_storage_disk"
    caching            = "ReadWrite"
    create_option      = "FromImage"
    managed_disk_type  = "Standard_LRS"
  }

  os_profile {
    computer_name  = "myvm"
    admin_username = "azureuser"
    admin_password = "MyComplexPassword"
  }

  os_profile_windows_config {
  }

  # other configuration settings...

}

resource "azurerm_virtual_machine" "new_vm" {
  count = data.external.vm_exists.result.value == true ? 0 : 1
  name                = var.vm_name
  resource_group_name = var.resource_group_name
  location            = "eastus"
}