What is the 20 instance(s) are already running error in my auto scaling activities?
By default, EC2 will only let each AWS account launch 20 instances. To launch more instances than 20, AWS has to enable a different number on your account. Even if you have auto scaling set up, EC2 will still impose the 20 limit, unless it is changed by AWS. The 20 instance(s) are already running error iindicates that you are hitting the limit.
You can request AWS to increase the number here: