How to Import an Azure Subnet Route Table Association into Terraform

Import Azure Subnet Route Table Association 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 Route Table Association 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_route_table_association.main
  id = "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/prod-rg/providers/Microsoft.Network/virtualNetworks/prod-vnet/subnets/app-subnet"
}

Example azurerm_subnet_route_table_association configuration

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

resource "azurerm_subnet_route_table_association" "main" {
  subnet_id      = azurerm_subnet.app.id
  route_table_id = azurerm_route_table.main.id
}

Gotchas when importing a Azure Subnet Route Table Association

• The import ID is the SUBNET's ARM resource ID, not the route table's; the association is stored as a property of the subnet.
• A subnet can be associated with only one route table, so there is exactly one association resource per subnet.
• Do not also configure the route table inline on the azurerm_subnet resource; managing the link both inline and through this resource produces a perpetual diff.
• The route table and the subnet's virtual network must reside in the same region and subscription.

Doing it manually with terraform import

The native approach is to write the azurerm_subnet_route_table_association block by hand, then run terraform import azurerm_subnet_route_table_association.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