I have the following situation: I have 1 Rails App that has 2 domains, each of these domains has multiple/dynamical subdomains. This app is in AWS using a load-balanced Elastic
To add multiple Elastic Load Balancers (ELB) to an Elastic Beanstalk (EB) application, you need to add the additional ELB to the auto scaling group of the EB app.
The easiest way to achieve this is through the AWS CLI (https://aws.amazon.com/cli/):
aws autoscaling attach-load-balancers --auto-scaling-group-name
Of course this can be done in the AWS Console, too:
For your convenience, you can see where you need to click for all of the 5 steps (don't forget to save!)
For me this works also on eb-generated auto scaling groups (Region: eu-central-1).
This might not have been available at the time of the question, but it is now.