Aws autoscaling group in private subnet, private communication? I have a scenario -
I have configured my frontend application in one autoscaling group and my backend application is in another autoscaling group. I'm using the load balancer also. But I don't want API call from front end to the backend over the internet.
How Can I make front end application in autoscaling group to communicate privately with backend application which also in another autoscaling group?
I am assuming that the backend application has been set up in its own subnet that has been configured for private IP addresses only.  If not I would recommend that you do that as a starter for 10.

With that in place, you could set up an internal application load balancer to work on private only and have your backend ASG use this.
from the AWS docs
https://docs.aws.amazon.com/AmazonECS/latest/developerguide/create-application-load-balancer.html