I'm trying to build an object in the locals tf file that take the values obtained from data.azurerm_subnet.vnet-subnets to be used down the line for a web app deployment. However, I cannot get the index function to work. The web app deployment needs to take a "priority" in the form of a number. Any help is greatly appreciated.

locals.tf

locals {
  webapp_vnet_subnets = {
    for key, val in data.azurerm_subnet.vnet-subnets :
    key => { for subnet in val : subnet => {
      name      = subnet.name
      subnet_id = subnet.id
      priority  = index(tolist(data.azurerm_subnet.vnet-subnets), subnet.name) + 100
      }
    }
  }
}

data.tf

data "azurerm_virtual_network" "vnet" {
  name                = var.prod_vnet
  resource_group_name = var.prod_vnet_rg
}
data "azurerm_subnet" "vnet-subnets" {
  for_each             = toset(data.azurerm_virtual_network.vnet.subnets)
  name                 = each.value
  virtual_network_name = data.azurerm_virtual_network.vnet.name
  resource_group_name  = data.azurerm_virtual_network.vnet.resource_group_name
}

main.tf

module "ncs-management-service" {
  source  = "app.terraform.io//windows-web-app/azurerm"
  version = "1.0.0"

  webapp_name         = "web-app-p-001"
  resource_group_name = data.azurerm_resource_group.paas-rg.name
  location            = data.azurerm_resource_group.paas-rg.location
  app_service_plan_id = module.asp.id
  tags = {
    "Billing Project" = var.billing_tag
    Environment       = var.environment_tag
    Component         = "App Service Plan"
    System            = var.system_tag
    Terraform         = var.terraform_tag
  }

  settings = {
    subnet_id                     = data.azurerm_subnet.vnet-subnets[var.prod_subnet].id
    vnet_route_all_enabled        = true
    always_on                     = true
    use_32_bit_worker             = false
    minimum_tls_version           = 1.2
    worker_count                  = 1
    current_stack                 = "dotnet"
    dotnet_version                = "v8.0"
    deployment_slot_enabled       = true
    ip_restriction_default_action = "Deny"
    network_rulesets = {
      ip_rule              = []
      virtual_network_rule = [local.webapp_vnet_subnets]
    }
  }
}

Error

│ Error: Unsupported attribute
│
│   on locals.tf line 7, in locals:
│    7:       priority  = index(tolist(data.azurerm_subnet.vnet-subnets), subnet.name) + 100
│
│ Can't access attributes on a primitive-typed value (string).

I'm trying to build an object in the locals tf file that take the values obtained from data.azurerm_subnet.vnet-subnets to be used down the line for a web app deployment. However, I cannot get the index function to work. The web app deployment needs to take a "priority" in the form of a number. Any help is greatly appreciated.

locals.tf

locals {
  webapp_vnet_subnets = {
    for key, val in data.azurerm_subnet.vnet-subnets :
    key => { for subnet in val : subnet => {
      name      = subnet.name
      subnet_id = subnet.id
      priority  = index(tolist(data.azurerm_subnet.vnet-subnets), subnet.name) + 100
      }
    }
  }
}

data.tf

data "azurerm_virtual_network" "vnet" {
  name                = var.prod_vnet
  resource_group_name = var.prod_vnet_rg
}
data "azurerm_subnet" "vnet-subnets" {
  for_each             = toset(data.azurerm_virtual_network.vnet.subnets)
  name                 = each.value
  virtual_network_name = data.azurerm_virtual_network.vnet.name
  resource_group_name  = data.azurerm_virtual_network.vnet.resource_group_name
}

main.tf

module "ncs-management-service" {
  source  = "app.terraform.io//windows-web-app/azurerm"
  version = "1.0.0"

  webapp_name         = "web-app-p-001"
  resource_group_name = data.azurerm_resource_group.paas-rg.name
  location            = data.azurerm_resource_group.paas-rg.location
  app_service_plan_id = module.asp.id
  tags = {
    "Billing Project" = var.billing_tag
    Environment       = var.environment_tag
    Component         = "App Service Plan"
    System            = var.system_tag
    Terraform         = var.terraform_tag
  }

  settings = {
    subnet_id                     = data.azurerm_subnet.vnet-subnets[var.prod_subnet].id
    vnet_route_all_enabled        = true
    always_on                     = true
    use_32_bit_worker             = false
    minimum_tls_version           = 1.2
    worker_count                  = 1
    current_stack                 = "dotnet"
    dotnet_version                = "v8.0"
    deployment_slot_enabled       = true
    ip_restriction_default_action = "Deny"
    network_rulesets = {
      ip_rule              = []
      virtual_network_rule = [local.webapp_vnet_subnets]
    }
  }
}

Error

│ Error: Unsupported attribute
│
│   on locals.tf line 7, in locals:
│    7:       priority  = index(tolist(data.azurerm_subnet.vnet-subnets), subnet.name) + 100
│
│ Can't access attributes on a primitive-typed value (string).

• azure
• terraform
• terraform-provider-azure
• azure-rm

• how do i do that? i still get this error 'priority = 100 + index(keys(data.azurerm_subnet.vnet-subnets), subnet_name) │ A reference to a resource type must be followed by at least one attribute access, specifying the resource name' – NickP Commented Mar 13 at 12:44
• Try this priority = 100 + index(keys({ for k, v in data.azurerm_subnet.vnet-subnets : k => v }), subnet_name) This ensures keys() extracts subnet names correctly before using index() @NickP – Vinay B Commented Mar 13 at 13:20
• Error: priority = 100 + index(keys({ for k, v in data.azurerm_subnet.vnet-subnets : k => v }), subnet_name) │ │ A reference to a resource type must be followed by at least one attribute access, specifying the resource name. – NickP Commented Mar 13 at 13:51
• this fixed it locals { webapp_vnet_subnets = { for k, v in data.azurerm_subnet.vnet-subnets : k => { name = v.name subnet_id = v.id priority = 100 + index(keys({ for k, v in data.azurerm_subnet.vnet-subnets : k => v }), v.name) } } } – NickP Commented Mar 13 at 13:53
• this now gives me an output in the format, webapp_vnet_subnets = { "subnet1" = { name = "subnet1" subnet_id = "subnet1_id" priority = 100 } "subnet2" = { name = "subnet2" subnet_id = "subnet2_id" priority = 101 }} How can i omit the keys for the resource needs it in a list format like so: webapp_vnet_subnets = [ { name = "subnet1" subnet_id = "subnet1_id" priority = 100 }, { name = "subnet2" subnet_id = "subnet2_id" priority = 101 }] – NickP Commented Mar 13 at 14:01

1 Answer 1

Build Terraform variable object based off data block or varaiable

Glad to know it works for you @NickP posting this approach as solution so that it will be helpful for the community.

You define local object, Terraform pulls subnet information dynamically using

data "azurerm_subnet" "vnet-subnets" {
  for_each             = toset(data.azurerm_virtual_network.vnet.subnets)
  name                 = each.value
  virtual_network_name = data.azurerm_virtual_network.vnet.name
  resource_group_name  = data.azurerm_virtual_network.vnet.resource_group_name
}

Here, the use of for each ensure that it fetch every dynamically & data source stores the subnet objects mapped by their names.

With this, we can assume keys are subnet name and values are objects of subnet.

Now as discussed in comments rewrite the locals in the given format below

webapp_vnet_subnets = {
  for k, v in data.azurerm_subnet.vnet-subnets :
  k => {
    name      = v.name
    subnet_id = v.id
    priority  = 100 + index(keys({ for k, v in data.azurerm_subnet.vnet-subnets : k => v }), v.name)
  }
}

This creates a valid list of subnet names as expected.

Alternatively, the suggestion you mentioned

filtered_list = values(local.webapp_vnet_subnets)

which in general helps to extract only the value local.webapp_vnet_subnet

Will return only the values in list format, removing the keys.

Refer:

https://dev.to/sre_panchanan/terraform-for-expressions-5hcc

https://developer.hashicorp/terraform/language/values/outputs