Can't delete an instance group created by GKE nodepool that's in use by a backend service

[rakeshnetsil]

I'm using the terraform to manage the GKE cluster setup. I want to update the instance size of the worker nodes that would re-create google_container_node_pol. But that steps failing because below error because instance groups attached with GCP LB backend not detaching by terraform.

oogle_container_node_pool.new_container_cluster_node_pool.0: Error waiting for deleting GKE NodePool:
(1) Google Compute Engine: The instance_template resource 'projects/XXX-XXX-XXXX/global/instanceTemplates/gke-XXX-XXX-us-west-XXXXXX-53369325' is already being used by 'projects/XXXX-XXXX-XXXXX/zones/us-west1-b/instanceGroupManagers/gke-XXXXX-XXXX-us-west-XXXXX-XXXXX-us-west-53369325-grp'

Finally, we have to manually remove the instance groups entries from GCP LB backend, plan and apply again to re-create the node pool with new instance type.