Function app uses the latest supported runtime version (~4)

# Minimal Function App with runtime set to v4 (~4) - use azurerm_linux_function_app or azurerm_windows_function_app
resource "azurerm_resource_group" "example" {
  name     = "<example_resource_name>"
  location = "eastus"
}

resource "azurerm_storage_account" "example" {
  name                     = "<example_resource_name>"
  resource_group_name      = azurerm_resource_group.example.name
  location                 = azurerm_resource_group.example.location
  account_tier             = "Standard"
  account_replication_type = "LRS"
}

resource "azurerm_service_plan" "example" {
  name                = "<example_resource_name>"
  resource_group_name = azurerm_resource_group.example.name
  location            = azurerm_resource_group.example.location
  os_type             = "Linux"
  sku_name            = "Y1"
}

resource "azurerm_linux_function_app" "example" {
  name                       = "<example_resource_name>"
  location                   = azurerm_resource_group.example.location
  resource_group_name        = azurerm_resource_group.example.name
  service_plan_id            = azurerm_service_plan.example.id
  storage_account_name       = azurerm_storage_account.example.name
  storage_account_access_key = azurerm_storage_account.example.primary_access_key

  site_config {}

  app_settings = {
    FUNCTIONS_EXTENSION_VERSION = "~4" # Critical: ensures the Function App uses runtime ~4
  }
}

// Set Azure Functions runtime to v4 for an existing Function App
resource functionApp 'Microsoft.Web/sites@2022-09-01' existing = {
  name: '<example_resource_name>'
}

resource appSettings 'Microsoft.Web/sites/config@2022-09-01' = {
  name: '${functionApp.name}/appsettings'
  properties: {
    FUNCTIONS_EXTENSION_VERSION: '~4' // Critical: ensures the Function App uses runtime ~4
  }
}