Failed to create aks using existing vnet - terraform

Question

I'm trying to create aks using terraform; the catch is I have already vnet and subnet created, I need to have the cluster created in that network.
When executing this code I'm getting an error:
locals {
environment = "prod"
resource_group = "hnk_rg_poc"
vnet_subnet_cidr = ["10.3.1.0/24"]
}
#Existing vnet with address space "10.3.1.0/24"
data "azurerm_virtual_network" "existing-vnet" {
name = "${var.vnet}"
resource_group_name = local.resource_group
}
#subnets
resource "azurerm_subnet" "vnet_subnet_id" {
name = "${var.vnet_subnet_id}"
resource_group_name = local.resource_group
address_prefixes = local.vnet_subnet_cidr
virtual_network_name = data.azurerm_virtual_network.existing-vnet.name
}
vnet_subnet_id = data.azurerm_subnet.vnet_subnet_id.id

Answer 1

As you are already having a existing Vnet and Subnet to be used by the AKS cluster , you have to use data block instead of resource block for the subnet.
You can use the below to create a basic aks cluster using your existing Vnet and Subnet:
provider "azurerm" {
features {}
}
#local vars
locals {
environment = "test"
resource_group = "resource_group_name"
name_prefix = "name-aks"
}
#Existing vnet with address space
data "azurerm_virtual_network" "base" {
name = "existing-vnet"
resource_group_name = local.resource_group
}
#existing subnet to be used by aks
data "azurerm_subnet" "aks" {
name = "existing-subnet"
resource_group_name = local.resource_group
virtual_network_name = data.azurerm_virtual_network.base.name
}
#kubernetes_cluster
resource "azurerm_kubernetes_cluster" "base" {
name = "${local.name_prefix}-${local.environment}"
location = data.azurerm_virtual_network.base.location
resource_group_name = data.azurerm_virtual_network.base.resource_group_name
dns_prefix = "dns-${local.name_prefix}-${local.environment}"
network_profile {
network_plugin = "azure"
}
default_node_pool {
name = "default"
node_count = 1
vm_size = "Standard_D2_v2"
vnet_subnet_id = data.azurerm_subnet.aks.id
}
identity {
type = "SystemAssigned"
}
}
Output: (Terraform Plan)