How to conditionally skip a part of terraform resource from being created/implemented using terrraform

Question

How to conditionally skip a part of terraform resource from being created/implemented using terraform?

# main.tf file
locals {
  vnet_type = (var.vnet_type != "" ? var.vnet_type : "None")
}

data "azurerm_virtual_network" vnet {
  name = "testvnet"
  resource_group_name = "rest1"
}
  
data "azurerm_subnet" subnets {
  name = "testSubnet"
   resource_group_name  = "rest1"
   virtual_network_name = data.azurerm_virtual_network.vnet.name

}


resource "azurerm_api_management" "apim_demo" {
  name                = "test-apim"
  location            = "East US"
  resource_group_name = "rest1"
  publisher_name      = "admin"
  publisher_email     = "[email protected]"

  sku_name = "Developer_1"

  identity {
    type = "SystemAssigned"
  }

 # vnet_Type can be External, None or Internal
 virtual_network_type = local.vnet_type
virtual_network_configuration {
  subnet_id = data.azurerm_subnet.subnets.id
}

}

# variables.tf file
variable "vnet_type" {}

# terraform.tfvars file
vnet_type = "External"

I have three (dev, stg and prod) environments where I want to apply below block/part of tf code to dev & stg environments skip it for prod environment.

How do I achieve above scenario using conditional expression or something in terraform ?

 virtual_network_type = local.vnet_type
virtual_network_configuration {
  subnet_id = data.azurerm_subnet.subnets.id
}

Answer 1

Generally you would use null and dynamic blocks:

virtual_network_type = var.env == "prod" ? local.vnet_type : null


dynamic "virtual_network_configuration" {
   for_each = var.env == "prod" ? [1] : []
   content {
     subnet_id = data.azurerm_subnet.subnets.id
   }
}