How load balancer discovers new instances that are added?

i am having an alb which is configured to load balance a target group (instance based). there is also an auto scaling policy defined with same alb for 80% cpu utilisation. the servers are running on port 8080 and the same is defined in the target group.

1. i want to understand how and when alb checks what is cpu utilisation of the instances?
2. lets say the cpu utilisation becomes > 80%, a new instance would be launched. how does the alb discovers it?

The ALB does not monitor the CPU usage of instances at all. The Autoscaling Group monitors the CPU usage of the instances, and adds or removes instances as needed to maintain your desired CPU usage. When the Autoscaling Group adds or removes instances, it updates the instances in the Target Group. The ALB simply checks the Target Group for the list of instances it can send traffic to.