Manually Detaching Instances from Elastigroups
You can simply detach the instance using the Console UI. This will remove the instance and create another:
In the dialog, make sure to keep "Decrement capacity" unchecked if you want a replacement instances to be launched.
Draining Timeout - Specify the time to keep the instance active for the before terminating it.
Decrement Group's Capacity - Change the group Instance count Target reducing it by a single instance - This will mean no replacement instance will be launched.
Lock an instance
You can Lock specific instances to prevent them from being scaled down during autoscaling. Simply select the instance you want to lock and use the lock icon
You can then define the time for the instance to be locked
Note: This will protect the instance from Scaling action - however, this will not prevent a spot interruption if one occurs.