Using TF to attach block volumes over a loop

Summary

I can use Terraform to create a set of identical compute instances but am struggling to attach a block volume to each

Content

I have used Terraform's count meta-parameter to provision a set of indentical compute instances:

resource "oci_core_instance" "myserver" {

count = "${var.qty_servers}"

display_name = "myserver${count.index}" ...

I have also used the same approach to create a block storage volume for each.

However I now need to attach the instance's extra volume to each instance. I'm trying something like this:

resource "oci_core_volume_attachment" "data-01" {

count = "${var.qty_servers}"

attachment_type = "paravirtualized"

instance_id = "${oci_core_instance.myserver.*.id}"