I am going to buy one AWS Reserved Instance and launch several EC2 instances. But these EC2 instances would not be running across time range. For example, instance 1 will be running from 00:00 to 11:59 and then be stopped. instance 2 will be running from 12:00 to 24:59 and then be stopped.
I'd like to know if only one Reserved Instance can apply to this two instances?
Thank you very much.
In short : Yes
Long: Yes, the same Reserved Instance (RI) would apply to both the instances because RI is just a billing concept. It is not specifically associated with any instance. The RI is automatically associated with any running instance. The instance chosen is such that your bill is the lowest.
So if you buy say 2 RIs and you run 4 instances at a time which match the RI criteria (instance-type, tenancy, region/availability zone and platform), the RI discount is automatically applied to any 2 of them.
Similarily, if you have 1 RI and 2 instances which match the criteria (the 4 attributes mentioned above) but only one instance is in running state at a time (others are in stopped state, not terminated) then yes, the RI discount will apply to both of them.
Just make sure that both instances are not running at the same time & both match the RI attributes.
Edit 1
AWS Billing automatically applies your RI’s discounted rate when attributes of EC2 instance usage match attributes of an active RI.
Refer this link. If you need further clarification/confirmation, you could contact AWS Customer Support by raising an Account & Billing Support case from your AWS Support center. You do not need to buy a support plan to raise billing cases & RIs are just a billing concept.
