Allow Application Gateway Backend pool pointing at a specific VM - azure

Question

How do we add virtual machine as target in backend pool of an Application Gateway using terraform code ?
What property I should use in the following code to point at particular virtual Machine ?
resource "azurerm_application_gateway" "network" {
name = "example-appgateway"
resource_group_name = "${azurerm_resource_group.test.name}"
location = "${azurerm_resource_group.test.location}"
sku {
name = "Standard_Small"
tier = "Standard"
capacity = 2
}
gateway_ip_configuration {
name = "my-gateway-ip-configuration"
subnet_id = "${azurerm_subnet.frontend.id}"
}
frontend_port {
name = "${local.frontend_port_name}"
port = 80
}
frontend_ip_configuration {
name = "${local.frontend_ip_configuration_name}"
public_ip_address_id = "${azurerm_public_ip.test.id}"
}
backend_address_pool {
name = "${local.backend_address_pool_name}"
}
backend_http_settings {
name = "${local.http_setting_name}"
cookie_based_affinity = "Disabled"
port = 80
protocol = "Http"
request_timeout = 1
}
http_listener {
name = "${local.listener_name}"
frontend_ip_configuration_name = "${local.frontend_ip_configuration_name}"
frontend_port_name = "${local.frontend_port_name}"
protocol = "Http"
}
request_routing_rule {
name = "${local.request_routing_rule_name}"
rule_type = "Basic"
http_listener_name = "${local.listener_name}"
backend_address_pool_name = "${local.backend_address_pool_name}"
backend_http_settings_name = "${local.http_setting_name}"
}
}
The backend_address_pool block supports:
name - (Required) User defined name for a backend address pool.
ip_addresses - (Optional) List of public IPAdresses, or internal IP
addresses in a backend address pool.
fqdns - (Optional) List of FQDNs in a backend address pool

Answer 1

Terraform is a bit silly in this regard, and you have to use a separate proxy resource (which doesnt even exist in Azure) to configure this:
resource "azurerm_resource_group" "test" {
name = "example-resources"
location = "West Europe"
}
resource "azurerm_virtual_network" "test" {
name = "example-network"
address_space = ["10.0.0.0/16"]
location = "${azurerm_resource_group.test.location}"
resource_group_name = "${azurerm_resource_group.test.name}"
}
resource "azurerm_subnet" "frontend" {
name = "frontend"
resource_group_name = "${azurerm_resource_group.test.name}"
virtual_network_name = "${azurerm_virtual_network.test.name}"
address_prefix = "10.254.0.0/24"
}
resource "azurerm_subnet" "backend" {
name = "backend"
resource_group_name = "${azurerm_resource_group.test.name}"
virtual_network_name = "${azurerm_virtual_network.test.name}"
address_prefix = "10.254.2.0/24"
}
resource "azurerm_public_ip" "test" {
name = "example-pip"
location = "${azurerm_resource_group.test.location}"
resource_group_name = "${azurerm_resource_group.test.name}"
allocation_method = "Dynamic"
}
# since these variables are re-used - a locals block makes this more maintainable
locals {
backend_address_pool_name = "${azurerm_virtual_network.test.name}-beap"
frontend_port_name = "${azurerm_virtual_network.test.name}-feport"
frontend_ip_configuration_name = "${azurerm_virtual_network.test.name}-feip"
http_setting_name = "${azurerm_virtual_network.test.name}-be-htst"
listener_name = "${azurerm_virtual_network.test.name}-httplstn"
request_routing_rule_name = "${azurerm_virtual_network.test.name}-rqrt"
}
resource "azurerm_application_gateway" "network" {
name = "example-appgateway"
resource_group_name = "${azurerm_resource_group.test.name}"
location = "${azurerm_resource_group.test.location}"
removed for brievity, check full example at the link below
}
# binding happens here
resource "azurerm_network_interface_application_gateway_backend_address_pool_association" "test" {
network_interface_id = "${azurerm_network_interface.test.id}"
ip_configuration_name = "testconfiguration1"
backend_address_pool_id = "${azurerm_application_gateway.test.backend_address_pool.0.id}"
}
Reading:
https://www.terraform.io/docs/providers/azurerm/r/network_interface_application_gateway_backend_address_pool_association.html

Answer 2

If someone will be looking at adding App Service to backend. This is following what you need to do:
backend_address_pool {
name = local.backend_address_pool_name
fqdns = ["${azurerm_function_app.function_app.name}.azurewebsites.net"]
}