GCP MIG wait for instances bootstrap

I'm using terraform to create MIG:

resource "google_compute_region_instance_group_manager" "bar" {
  provider = google-beta

  version {
    name = "${var.db_instance_name}-mig"
    instance_template = google_compute_instance_template.template.self_link
  }

  wait_for_instances = "true"
  ...

}

I want GCP MIG to wait for my instances to give a success/false signal so that instance/MIG is in "creation state" during my bootstrap scripts(given in instance_template) execution. This would prevent Rolling Update from killing my application.

Currently Rolling Update (Substitute replacement method) will add new instances, their status will quickly be set to RUNNING, and my old instances will be removed. I need Rolling Update to wait until my application actually run on new instances.


I'm basically looking for GCP alternative of AWS ASG CreationPolicy:

Resources:
  FooAutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    CreationPolicy:
      ResourceSignal:
        Count: 3

Found Runtime Configurator Waiter, but it works similarly to AWS Wait Stack Create Complete, and it's not something I want.