Terraform: Error: Invalid index operation - azure

Question

I am using Terraform 0.14 for to automate the creation of some Azure resources.
I am trying to create assign a pull role to an Azure Kubernetes cluster to pull images from an Azure container registry using a Managed system identity
Here is my code
Azure Kubernetes cluster (main.tf file)
resource "azurerm_kubernetes_cluster" "akc" {
name = var.cluster_name
location = var.location
resource_group_name = var.resource_group_name
dns_prefix = var.dns_prefix
kubernetes_version = var.kubernetes_version
api_server_authorized_ip_ranges = var.api_server_authorized_ip_ranges
identity {
type = "SystemAssigned"
}
}
Azure Kubernetes cluster (outputs.tf file)
output "principal_id" {
value = azurerm_kubernetes_cluster.akc.identity[0]["principal_id"]
}
Azure role assignment (main.tf file)
# Create a role assignment
resource "azurerm_role_assignment" "ara" {
scope = var.scope
role_definition_name = var.role_definition_name
principal_id = var.principal_id
}
Test environment (main.tf file)
# Create azure kubernetes cluster
module "azure_kubernetes_cluster" {
source = "../modules/azure-kubernetes-cluster"
cluster_name = var.cluster_name
location = var.location
dns_prefix = var.dns_prefix
resource_group_name = var.resource_group_name
kubernetes_version = var.kubernetes_version
node_count = var.node_count
min_count = var.min_count
max_count = var.max_count
os_disk_size_gb = "100"
max_pods = "110"
vm_size = var.vm_size
aad_group_name = var.aad_group_name
vnet_subnet_id = var.vnet_subnet_id
}
# Create azure container registry
module "azure_container_registry" {
source = "../modules/azure-container-registry"
container_registry_name = var.container_registry_name
resource_group_name = var.resource_group_name
location = var.location
sku = var.sku
admin_enabled = var.admin_enabled
}
# Create azure role assignment
module "azure_role_assignment" {
source = "../modules/azure-role-assignment"
scope = module.azure_container_registry.acr_id
role_definition_name = var.role_definition_name
principal_id = module.azure_kubernetes_cluster.principal_id
}
However, when I run the terraform plan command, I get the error below:
Error: Invalid index operation
on ../modules/aks-cluster/outputs.tf line 14, in output "principal_id":
14: value = azurerm_kubernetes_cluster.cluster.identity[0]["principal_id"]
Only attribute access is allowed here. Did you mean to access attribute
"principal_id" using the dot operator?
Trying to figure out the solution to this.

Answer 1

I later figured out the solution to the error. Some modifications were made in Terraform 0.12 and later versions on how index operations are called. So rather than this:
Azure Kubernetes cluster (outputs.tf file)
output "principal_id" {
value = azurerm_kubernetes_cluster.akc.identity[0]["principal_id"]
}
It will be this:
Azure Kubernetes cluster (outputs.tf file)
output "principal_id" {
value = azurerm_kubernetes_cluster.akc.identity.*.principal_id
}
And also instead of this:
Test environment (main.tf file)
# Create azure role assignment
module "azure_role_assignment" {
source = "../modules/azure-role-assignment"
scope = module.azure_container_registry.acr_id
role_definition_name = var.role_definition_name
principal_id = module.azure_kubernetes_cluster.principal_id
}
It will be this:
Test environment (main.tf file)
# Create azure role assignment
module "azure_role_assignment" {
source = "../modules/azure-role-assignment"
scope = module.azure_container_registry.acr_id
role_definition_name = var.role_definition_name
principal_id = module.azure_kubernetes_cluster.principal_id[0]
}
Resources: Invalid index when referencing output from module in 0.12
That's all
I hope this helps