Terraform conditional creation of Service endpoint for a subnet - azure

Question

I have a terraform script for creating a virtual network and subnets in azure. The code inherits a module which has the both creation of vnet and subnet. I am trying to create a VNET and two subnet, but want to enable service end point for a specific subnet only. Need help on how to do it
module "vnet" {
source = "./modules/VirtualNetwork"
VirtualNetwork_Name = "${var.prefix}-${var.resource_group_name}-VNET1"
Resource_Group_Name = azurerm_resource_group.resource_group.name
Location = azurerm_resource_group.resource_group.location
VirtualNetwork_AddressSpace = ["10.4.0.0/23"]
Subnet_Name = ["snet-1","snet-2"]
Subnet_Addresses = ["10.4.0.0/24","10.4.1.0/24"]
Service_Endpoints = vnet.Subnet_Name == "snet-1" ? ["Microsoft.AzureCosmosDB"] : [""]
if subnet=="snet-1" then ["Microsoft.AzureCosmosDB"] else ["nothing"]
Tags = {
environment = "prod"
resource = "VNET"
cost_center = "Test Cost Ceneter"
}
}
The below code is for network module
# Creates the virtual network for the resources
resource "azurerm_virtual_network" "vnet" {
name = var.VirtualNetwork_Name
location = var.Location
resource_group_name = var.Resource_Group_Name
address_space = var.VirtualNetwork_AddressSpace
tags = var.Tags
}
# Create two subnet for the vnet
resource "azurerm_subnet" "subnet" {
name = var.Subnet_Name[count.index]
address_prefix = var.Subnet_Addresses[count.index]
resource_group_name = var.Resource_Group_Name
virtual_network_name = azurerm_virtual_network.vnet.name
count = length(var.Subnet_Name)
# service_endpoints = ["Microsoft.AzureCosmosDB"]
service_endpoints = var.Service_Endpoints
}

Answer 1

According to your requirement, you just want to enable a service endpoint for a specific subnet only. You can set the conditional-expressions in the azurerm_subnet block.
You could change the code like this and I have validated it on my side.
main.if in the root directory.
variable "subnet_name" {
default = ["subnet1","subnet2"]
}
# retrieve a specific subnet via the index of subnet list.
locals {
subnet_name_enable_service_endpoint = element(var.subnet_name,0)
}
...
module "vnet" {
source = "./modules/VirtualNetwork"
VirtualNetwork_Name = "${var.prefix}-${var.resource_group_name}-VNET1"
Resource_Group_Name = azurerm_resource_group.main.name
Location = azurerm_resource_group.main.location
VirtualNetwork_AddressSpace = ["10.4.0.0/23"]
Subnet_Addresses = ["10.4.0.0/24","10.4.1.0/24"]
Subnet_Name = var.subnet_name
specfic_subnet_name = local.subnet_name_enable_service_endpoint
Service_Endpoints = ["Microsoft.AzureCosmosDB"]
Tags = {
environment = "prod"
resource = "VNET"
cost_center = "Test Cost Ceneter"
}
}
Network module configuration is in the path ./modules/VirtualNetwork.
# declare a variable for accepting the specific subnet.
variable "specfic_subnet_name" {
}
...
#Create Virtual Network in Primary Resource Group
resource "azurerm_virtual_network" "primary" {
name = var.VirtualNetwork_Name
resource_group_name = var.Resource_Group_Name
address_space = var.VirtualNetwork_AddressSpace
location = var.Location
tags = var.Tags
}
#Create Subnet in Virtual Network
resource "azurerm_subnet" "primary" {
count = length(var.Subnet_Name)
name = var.Subnet_Name[count.index]
resource_group_name = var.Resource_Group_Name
virtual_network_name = azurerm_virtual_network.primary.name
address_prefixes = [element(var.Subnet_Addresses,count.index)]
service_endpoints = element(var.Subnet_Name,count.index) == var.specfic_subnet_name ? var.Service_Endpoints : [""]
}

Answer 2

./modules/VirtualNetwork only the subnet creation part
# Create two subnet for the vnet
resource "azurerm_subnet" "subnet" {
name = var.Subnet_Name[count.index]
address_prefix = var.Subnet_Addresses[count.index]
resource_group_name = var.Resource_Group_Name
virtual_network_name = azurerm_virtual_network.vnet.name
count = length(var.Subnet_Name)
service_endpoints = element(var.Service_Endpoints,count.index)
}
main.tf
module "vnet" {
source = "./modules/VirtualNetwork"
VirtualNetwork_Name = "${var.prefix}-${var.resource_group_name}-VNET1"
Resource_Group_Name = azurerm_resource_group.resource_group.name
Location = azurerm_resource_group.resource_group.location
VirtualNetwork_AddressSpace = ["10.4.0.0/23"]
Subnet_Name = ["snet-1","snet-2"]
Subnet_Addresses = ["10.4.0.0/24","10.4.1.0/24"]
Service_Endpoints = [["Microsoft.AzureCosmosDB",""], [""]]
}
The key is to pass the service end point as a list Service_Endpoints = [["Microsoft.AzureCosmosDB",""], [""]]. Based on the index of the subnet it will assign the service end point