I have a fresh AWS account with Reserved Capacity of 15 EC2 instances of the same instance type in the same region primarily intended for EMR.
If I spawn a EMR cluster with 10 instances for 15 days and scale it up to 20 instances for the remaining 15 days, will I get charged $0?
If not, how will the final bill for EC2 for the month be calculated?
The reason why I am confused is that based on my understanding EC2 charges based on capacity consumed (in instance hours) and not on actual instances allocated. Since I'm reserving 15 instances worth of capacity, I would expect it to cost me a total of $0 since my overall monthly average consumption is worth 15 instances.
The Reserved EC2 Pricing documentation and most of the AWS price-calculation related material on the internet don't mention the use-case of dynamic scaling of instances in accounts with reserved capacity.