I am using a GCP region backend service to load balance across a set of instances in an unmanaged instance group. When I remove an instance from the group I want to know when I can safely delete the instance.
Connection draining is set to 0 seconds so as hinted by this post I am waiting until the instance no longer shows up in the health statuses of the backend service group and then waiting for an extra 60 seconds before deleting the instance; I assume the 60 seconds is required for the health status decision to be applied across GCP, but the only place I can find this time period mentioned is here and here, neither of which are definitive.
Is there any way to tell through the GCP APIs when I can safely remove an instance or do I need to make this decision using instance metrics (e.g. by waiting until no new connections have been made for a period of time).