How to specify an explicit "computer_name" in terraform azurerm

Question

I have defined computer name variable in file.tfvar file, when do terraform apply i got error like :

This is my code:

in main.tf:

resource "azurerm_windows_virtual_machine" "vm-report_identifier" {
name                = var.vm_reportserver_name
resource_group_name = azurerm_resource_group.main_resource_group_identitfier.name
location            = azurerm_resource_group.main_resource_group_identitfier.location
size                = var.vm_ReportingServices_size
admin_username      = var.vm_ReportingServices_admin_user
admin_password      = var.vm_ReportingServices_admin_pass
network_interface_ids = [azurerm_network_interface.nic_ReportingServices_identifier.id]

os_disk {
  caching              = var.vm_ReportingServices_osdisk_caching 
  storage_account_type = var.vm_ReportingServices_st_type
}

source_image_reference {
  publisher = var.vm_ReportingServices_publisher
  offer     = var.vm_ReportingServices_offer 
  sku       = var.vm_ReportingServices_sku
  version   = var.vm_ReportingServices_version
}
}

in variable.tf

# Virtual Machine-ReportingServices
variable "vm_reportserver_name" { type = string }
variable "vm_ReportingServices_size" { type = string }
variable "vm_ReportingServices_admin_user" {type = string}
variable "vm_ReportingServices_admin_pass" { type = string }
variable "vm_ReportingServices_osdisk_caching" { type = string }
variable "vm_ReportingServices_st_type" { type = string }
variable "vm_ReportingServices_publisher" { type = string }
variable "vm_ReportingServices_offer" { type = string }
variable "vm_ReportingServices_sku" { type = string }
variable "vm_ReportingServices_version" { type = string }

in file.tfvar

# Virtial Machine-ReportingServices
vm_reportserver_name = "reportserver-prod"
vm_ReportingServices_size = "Standard_D2s_v3"
vm_ReportingServices_admin_user = "reportserver-prod-admin"
vm_ReportingServices_admin_pass =  "Psdjhu31w0rd12945340!"
vm_ReportingServices_osdisk_caching = "ReadWrite"
vm_ReportingServices_st_type = "StandardSSD_LRS"
vm_ReportingServices_publisher =  "MicrosoftWindowsServer"
vm_ReportingServices_offer = "WindowsServer"
vm_ReportingServices_sku =  "2022-datacenter-azure-edition-smalldisk"
vm_ReportingServices_version = "latest"

azurerm_windows_virtual_machine.vm-report_identifier: Creating...

Error: unable to assume default computer name "computer_name" can be at most 15 characters, got 17. Please adjust the "name", or specify an explicit "computer_name"

with azurerm_windows_virtual_machine.vm-report_identifier, on main.tf line 379, in resource "azurerm_windows_virtual_machine" "vm-report_identifier": 379: resource "azurerm_windows_virtual_machine" "vm-report_identifier"

My ask is how to an explicitly specify "computer_name" to azurerm virtual machine in terraform

Answer 1

As mentioned above, computer_name can be at most 15 characters. We can see from your code that Terraform is trying to set the default computer_name from the resource name, which is 17 characters (reportserver-prod), hence invalid.

If the default computer_name is invalid, it has to be explicitly defined using the computer_name argument as follows:

main.tf

resource "azurerm_windows_virtual_machine" "vm-report_identifier" {
 name                = var.vm_reportserver_name
 resource_group_name = 
 azurerm_resource_group.main_resource_group_identitfier.name
 location            = 
 azurerm_resource_group.main_resource_group_identitfier.location
 size                = var.vm_ReportingServices_size
 computer_name       = var.vm_reportserver_computername
 admin_username      = var.vm_ReportingServices_admin_user
 admin_password      = var.vm_ReportingServices_admin_pass
 network_interface_ids = 
 [azurerm_network_interface.nic_ReportingServices_identifier.id]

 os_disk {
   caching              = var.vm_ReportingServices_osdisk_caching 
   storage_account_type = var.vm_ReportingServices_st_type
 }

 source_image_reference {
   publisher = var.vm_ReportingServices_publisher
   offer     = var.vm_ReportingServices_offer 
   sku       = var.vm_ReportingServices_sku
   version   = var.vm_ReportingServices_version
 }
}

add the following to variable.tf

variable "vm_reportserver_computername" { type = string }

add the following to file.tfvar

vm_reportserver_computername = "reportserverprd" #(15 characters)

See the attribute definition from the resource documentation:

computer_name - (Optional) Specifies the Hostname which should be used for this Virtual Machine. If unspecified this defaults to the value for the name field. If the value of the name field is not a valid computer_name, then you must specify computer_name. Changing this forces a new resource to be created.

You will then end up with different names for the Azure Resource and for the Windows hostname