Documentation: Follow the instructions on how to Set Up an Auto-Scaled and Load-Balanced Application
Notes: The instance, created outside of AutoScaling Group can be added to Elastic Load Balancer, but will not be monitored or managed by AutoScaling group.
Instance, created outside of AutoScaling Group can be marked as unhealthy by Elastic Load Balancer if the health check fails, but it will not cause AutoScaling Group to spawn a new instance.