Autoscaling: Dynamically creates or deletes VMs to meet the instance group target. The setting of 80% means that the autoscaler will kick in when operating at 80% of the HTTP(S) Load Balancer’s balancing mode setting. This can be based on connection rate or CPU utilization.
Cool-down period: How long to wait before collecting information from a new instance. This should be at least the time it takes to initialize the instance.
Autohealing: Allow for a health-check on each VM in the instance group. If the health-check fails, GCE will automatically attempt to restart the instance.