azurerm_route_table/Subnet association is dropped on update.

[TStraub-rms]

Terraform Version

terraform version 0.8.4

Affected Resource(s)

• azurerm_route_table

Terraform Configuration Files

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     = "${var.module_name}-Network-Infrastructure"
  location = "${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                = "${var.module_name}-RouteTable"
  location            = "${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"
}

Expected Behavior

Updating the route table should keep or update the subnet association of the table.

Actual Behavior

The initial terraform apply will create all the resources without an issue.

When updating the route table (by updating the tags for instance), the subnet association is dropped.

Steps to Reproduce

1. terraform apply a route table with at least one route.
2. update the module to include new or different tags.
3. 'terraform plan` will show the only modification was the tag updates.
4. terraform apply will update the tags, but remove the subnet association from the route table.

[TStraub-rms]

@stack72 Have you seen this issue? I took a stab at the PR but having trouble getting this resolved myself.

[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.