Fleet management

Fleet management is one of the main reasons for managing the EC2 instances for your application in an Auto Scaling Group. You can usually put all the healthy instance behind the load balancer and let it serve the traffic to the healthy instances. As discussed in an earlier chapter, if an EC2 instance becomes unhealthy, the load balancer will stop sending traffic to it, and you have to take appropriate action manually to ensure that instances are healthy and ready to serve traffic again. This is where Auto Scaling plays a vital role, even though you do not have any intention of scaling. Instead of running those EC2 instance independently behind the load balancer, if you add them as part of the Auto Scaling Group, Auto Scaling automatically manages the fleet behind your load balancer and you do not need to take any manual action if any one of the EC2 instances becomes unhealthy.

An Auto Scaling health check will detect an impaired instance and replace it with a healthy one...