How to fix Error: Error deleting Route Table: InUseRouteTableCannotBeDeleted in Terraform

TerraformINTERMEDIATEHIGH

The "InUseRouteTableCannotBeDeleted" error occurs when Terraform tries to delete an Azure route table that is still associated with a subnet. Azure prevents deletion of route tables that are actively in use, requiring proper disassociation before removal.

What this error means

This error means the Azure route table you are trying to delete is still associated with one or more subnets in your virtual network. Azure enforces this restriction as a safety measure to prevent accidental deletion of network infrastructure that is actively routing traffic. The route table must be fully disassociated from all subnets before it can be deleted.

How to fix "Error: Error deleting Route Table: InUseRouteTableCannotBeDeleted"

1Verify route table associations in Azure Portal

1. Navigate to the Azure Portal
2. Search for "Route tables" and select the problematic route table
3. In the left menu, click "Subnets"
4. Note all subnets currently associated with this route table
5. If no subnets are shown, the association may be managed differently - check your resource group for other references

2Update Terraform configuration to use azurerm_subnet_route_table_association

Instead of using inline route_table_id in azurerm_subnet:

hcl

# Bad approach (deprecated)
resource "azurerm_subnet" "example" {
  name           = "example-subnet"
  virtual_network_name = azurerm_virtual_network.example.name
  resource_group_name  = azurerm_resource_group.example.name
  address_prefixes     = ["10.0.1.0/24"]
  route_table_id       = azurerm_route_table.example.id  # Problematic
}

# Good approach (recommended)
resource "azurerm_subnet_route_table_association" "example" {
  subnet_id      = azurerm_subnet.example.id
  route_table_id = azurerm_route_table.example.id
}

This makes Terraform aware of the dependency and manages the association separately, allowing proper cleanup order during destroy.

3Add explicit depends_on to ensure correct deletion order

If you cannot change the resource structure, add explicit dependencies to your Terraform configuration:

hcl

resource "azurerm_route_table" "example" {
  name                = "example-rt"
  location            = azurerm_resource_group.example.location
  resource_group_name = azurerm_resource_group.example.name
}

resource "azurerm_subnet" "example" {
  name                 = "example-subnet"
  virtual_network_name = azurerm_virtual_network.example.name
  resource_group_name  = azurerm_resource_group.example.name
  address_prefixes     = ["10.0.1.0/24"]
  route_table_id       = azurerm_route_table.example.id
  depends_on           = [azurerm_route_table.example]
}

This tells Terraform to destroy the subnet before the route table.

4Manually disassociate the route table from subnets if needed

If immediate destruction is required, disassociate via Azure Portal:

1. Navigate to the virtual network containing the subnet
2. Go to Subnets in the left menu
3. Select the subnet that uses the problematic route table
4. In the Route table dropdown, select None
5. Click Save

Or via Azure CLI:

bash

az network vnet subnet update \
  --resource-group myResourceGroup \
  --vnet-name myVNet \
  --name mySubnet \
  --route-table null

Or via PowerShell:

powershell

$subnet = Get-AzVirtualNetworkSubnetConfig -Name mySubnet -VirtualNetwork (Get-AzVirtualNetwork -Name myVNet -ResourceGroupName myResourceGroup)
Set-AzVirtualNetworkSubnetConfig -Name $subnet.Name -VirtualNetwork (Get-AzVirtualNetwork -Name myVNet -ResourceGroupName myResourceGroup) -AddressPrefix $subnet.AddressPrefix -RouteTable $null

5Run terraform destroy again after disassociation

After manually disassociating the route table or updating your Terraform configuration:

bash

terraform plan -destroy
terraform destroy

The route table should now be deletable. If you still encounter the error, verify that:
- All subnets have been fully disassociated
- No dependent resources (like Azure SQL Managed Instance) are still using the route table
- The route table is not referenced in any Local Network Gateway prefixes

How to fix Error: Error deleting Route Table: InUseRouteTableCannotBeDeleted in Terraform

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How to fix "Error: Error deleting Route Table: InUseRouteTableCannotBeDeleted"

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