How to Import an Azure Subnet into Terraform

Import Azure Subnet with Terraback (recommended)

Terraback reverse-engineers your live infrastructure: it reads the Azure Networking resource with read-only credentials, generates the HCL, and produces the exact import block. Two commands take you from a live Azure Subnet to managed Terraform.

terraback scan all azure --subscription-id YOUR_ID

terraback azure import --method bulk

The Terraform import block

Terraback emits a Terraform 1.5+ import block like the one below. Because the block lives in your configuration, the import is reviewable in a pull request and repeatable across environments.

import {
  to = azurerm_subnet.app
  id = "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/prod-rg/providers/Microsoft.Network/virtualNetworks/prod-vnet/subnets/app"
}

Example azurerm_subnet configuration

Here is a realistic Azure Subnet block. Terraback generates a fuller version from your actual resource attributes; this is a minimal, valid starting point.

resource "azurerm_subnet" "app" {
  name                 = "app"
  resource_group_name  = "prod-rg"
  virtual_network_name = "prod-vnet"
  address_prefixes     = ["10.0.1.0/24"]
}

Gotchas when importing a Azure Subnet

• The subnet ID nests under its virtual network; you cannot import a subnet without the parent VNet path.
• If the parent VNet declares subnets inline, do not also manage them as separate azurerm_subnet resources.
• NSG and route table associations are separate azurerm_subnet_network_security_group_association and azurerm_subnet_route_table_association resources.
• address_prefixes (plural) replaced the older singular address_prefix argument.

Doing it manually with terraform import

The native approach is to write the azurerm_subnet block by hand, then run terraform import azurerm_subnet.example <import-id> for every resource, one at a time. That works for a handful of resources, but it does not scale: you author all the HCL yourself and repeat the command for each item. Terraback generates the HCL and the import blocks for your whole account in one pass.

Import other Azure resources