Auto Scaling Group

To increase ASG capacity use update-auto-scaling-group:

aws autoscaling update-auto-scaling-group --auto-scaling-group-name _name_ \
    --min-size 2 --desired-capacity 3 --max-size 10

To terminate an instance in an ASG, use terminate-instance-in-auto-scaling-group - also need to specify whether desired capacity should be changed.

aws autoscaling terminate-instance-in-auto-scaling-group --instance-id  _id_ \
    --should-decrement-desired-capacity