Unable to create new VNet in a specified resource group after checking its existence

Here I'm using data blocks for retrieve the information of Vnet if it already exist. If VNet is not existing than create a new one with the same name. I have defined everything properly.

data "azurerm_virtual_network" "existing_vnet" {
  name                = var.vnet_name
  resource_group_name = data.azurerm_resource_group.existing_rg.name
}

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

resource "azurerm_virtual_network" "my_vnet" {
  count = local.vnet_exists ? 0 : 1

  name                = var.vnet_name
  address_space       = var.address_space
  location            = data.azurerm_resource_group.existing_rg.location
  resource_group_name = data.azurerm_resource_group.existing_rg.name
}

But after running terraform apply it shows me an error of:

Error: Error: Virtual Network: (Name "axis_VN" / Resource Group "training") was not found
│ 
│   with data.azurerm_virtual_network.existing_vnet,
│   on main.tf line 24, in data "azurerm_virtual_network" "existing_vnet":
│   24: data "azurerm_virtual_network" "existing_vnet" {

can any one help me in this?

I was expecting that VNet would only create if it doesn't exit in the resource group

I tried to check with following code , to check for existing resources

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
}

It gives error as "resource not found " if it does not exist already .

For this External Data source can be used : external_external | Data Sources | hashicorp/external | Terraform Registry as Terraform does not check for preexisting resources.

Here almost any programming language can be used. One such example i tried to create VM if it does not exist.

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

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

Powershell code: 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" }'
      
    }

Initially checked only for non existence:It has to return true.

Then if the Vm doesnot exist , it will be created.

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"
}