azurerm_subnet does not track route_table_id association.

[carinadigital]

Terraform Version

Terraform v0.7.0

Affected Resource(s)

• azurerm_subnet

Terraform Configuration Files

resource "azurerm_resource_group" "test" {
    name = "acceptanceTestResourceGroup1"
    location = "West US"
}

resource "azurerm_virtual_network" "test" {
    name = "acceptanceTestVirtualNetwork1"
    address_space = ["10.0.0.0/16"]
    location = "West US"
    resource_group_name = "${azurerm_resource_group.test.name}"
}

resource "azurerm_subnet" "test" {
    name = "testsubnet"
    resource_group_name = "${azurerm_resource_group.test.name}"
    virtual_network_name = "${azurerm_virtual_network.test.name}"
    address_prefix = "10.0.1.0/24"
    route_table_id = "${azurerm_route_table.test.id}"
}

resource "azurerm_route_table" "test" {
    name = "acceptanceTestRouteTable1"
    location = "West US"
    resource_group_name = "${azurerm_resource_group.test.name}"
}

Debug Output

Panic Output

Expected Behavior

The plan should detect that the subnet is not associated with the route table.

Actual Behavior

No differences were detected.

Steps to Reproduce

1. terraform apply
2. Manually disassociate the subnet and route table (either azure cli or azure portal)
   Portal; You can disassociate by drilling down through ResourceGroup->RouteTable->Subnets-> Click on ... to dissassociate.
3. terraform plan

Important Factoids

References

[carinadigital]

The error is in the function resourceArmSubnetRead() . It doesn't have a section to read the subnet association from a routeTable object.

[stack72]

Hi @carinadigital

Is this still an issue?

P.

[carinadigital]

Yes. You are unable to change the Network Security Group on a subnet after initial creation.

[carinadigital]

Maybe see #9648 for more indepth information.

[TStraub-rms]

@carinadigital I ran this test with the terraform code block at the bottom of this comment to exploit this bug.

Terraform version

0.7.10

Reproduce Steps

Initial Apply

terraform apply with the no tags passed into the module.

tags = {}

Result:
Resource Group, Virtual Network, Subnet, and Route Table is create. 👍
The Route Table has the Subnet associated. 👍

Updating Apply

Update Terraform to add new tags to the module.

tags = {
    newtag = "I am a new tag"
}

Result:
Tags have been added to the Resource Group, Virtual Network, and Route Table.
However, the Routes in the Route Table have been dropped (was addressed and should be fixed in the next release here). ❗️

The Subnet is no longer associated to the Route Table (this is the bug). ❗️

Terraform Used

variable "tenant_id" {}
variable "client_id" {}
variable "client_secret" {}
variable "subscription_id" {}
variable "location" {}
variable "module_name" {}
variable "vnet_address_space" {}
variable "stack_subnet1" {}
variable "tags" {
  description = "(Optional) Tags to be assigned to every resource in the module."
  type        = "map"
  default     = {}
}

provider "azurerm" {
  tenant_id       = "${var.tenant_id}"
  subscription_id = "${var.subscription_id}"
  client_id       = "${var.client_id}"
  client_secret   = "${var.client_secret}"
}

resource "azurerm_resource_group" "module" {
  name     = "${var.module_name}-NI"
  location = "${var.location}"
  tags     = "${var.tags}"
}

resource "azurerm_virtual_network" "module" {
  name                = "${var.module_name}-Vnet1"
  resource_group_name = "${azurerm_resource_group.module.name}"
  address_space       = ["${var.vnet_address_space}"]
  location            = "${var.location}"
  tags                = "${var.tags}"
}

resource "azurerm_subnet" "subnet1" {
  name                 = "${var.module_name}-SubNet1"
  resource_group_name  = "${azurerm_resource_group.module.name}"
  virtual_network_name = "${azurerm_virtual_network.module.name}"
  address_prefix       = "${var.stack_subnet1}"
  route_table_id       = "${azurerm_route_table.module.id}"
}

resource "azurerm_route_table" "module" {
  name                = "${var.module_name}-RT"
  location            = "${var.location}"
  resource_group_name = "${azurerm_resource_group.module.name}"
  tags                = "${var.tags}"
}

resource "azurerm_route" "route_a" {
  name                = "Test Route A"
  resource_group_name = "${azurerm_resource_group.module.name}"
  route_table_name    = "${azurerm_route_table.module.name}"

  address_prefix         = "10.100.0.0/14"
  next_hop_type          = "VirtualAppliance"
  next_hop_in_ip_address = "10.10.1.1"
}

[TStraub-rms]

This issue came back and hit me again.
Can we get any traction on this?
Any way I can help progress this PR/Change?

Cheers!

[geofffranks]

+1

Just tried to remove a route table association from a subnet via terraform, and terraform said no changes were necessary.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.