How to do I set host.json in azurerm_linux_function_app?

Terraform Providers Azure
1

As an example, let’s say I rolled out an azurerm_linux_function_app with the following spec:

resource "azurerm_linux_function_app" "example" {
  name                       = var.cluster_name
  resource_group_name        = azurerm_resource_group.example.name
  location                   = azurerm_resource_group.example.location
  storage_account_name       = azurerm_storage_account.example.name
  storage_account_access_key = azurerm_storage_account.example.primary_access_key
  service_plan_id            = azurerm_service_plan.example.id

  identity {
    type = "SystemAssigned"
  }
  app_settings = {
    "ServiceBusConnection__fullyQualifiedNamespace" = "${local.service_bus_namespace}.servicebus.windows.net"
  }

  site_config {
    application_stack {
      python_version = "3.9"
    }
  }
}

If I navigate to “App files” on the resource in the Azure Portal, I can see that the following host.json has been created:

{
  "version": "2.0",
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[2.*, 3.0.0)"
  }
}

I don’t see any mention of this anywhere in the tf state though. I need to change this to the following so that I can use a service bus bindinf with a managed identity:

{
  "version": "2.0",
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[3.3.0, 4.0.0)"
  }
}

How can I set this using the azurerm terraform provider?

The only field I can find that remotely appears to deal with this is functions_extension_version, but changing this does not appear to have any affect that I can see. It is in any case by default "~4", so I would not expect that to lead to "version": "[2.*, 3.0.0)" to begin with.

2

I can override the individual settings in app_settings env vars:

app_settings = {
    "ServiceBusConnection__fullyQualifiedNamespace" = "${local.service_bus_namespace}.servicebus.windows.net"

    # instead of setting host.json (which doesn't seem possible?!) set the individual values here
    # see https://learn.microsoft.com/en-us/azure/azure-functions/functions-app-settings#azurefunctionsjobhost_
    # see https://learn.microsoft.com/en-us/azure/azure-functions/functions-host-json#sample-hostjson-file
    "AzureFunctionsJobHost__version"                  = "2.0"
    "AzureFunctionsJobHost__extensionBundle__id"      = "Microsoft.Azure.Functions.ExtensionBundle"
    "AzureFunctionsJobHost__extensionBundle__version" = "[3.*, 4.0.0)"
  }

But still don’t see how one can set host.json itself