Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm writing an app and had been paying an hourly rate for my EC2 instance, as I've needed to test. I decided I should just pay for a reserved instance to save money in the long run, but now that I have one, I'm confused about how I'm supposed to manage it. In the "Instances" section of the EC2 management console, I can see the instances that I've launched in the past, and I can stop/start them as I see fit. However, it seems the only way to view my reserved instance is to use the "Reserved Instances" drop-down, but this only seems to let me view them, but nothing else...

So, my question is, how can I do the same thing with my reserved instance(s) that I've been doing with my hourly instance(s)? I basically just want to associate my elastic IP with my reserved instance and install my server image on it.

share|improve this question
up vote 4 down vote accepted

How do I purchase and start up a Reserved Instance?

You purchase an EC2 Reserved Instance by calling the PurchaseReservedInstancesOffering API method. Launching a Reserved Instance is no different than launching an On-Demand Instance. You simply use the RunInstances command or launch an instance via the AWS Management Console. Amazon EC2 will optimally apply the cheapest rate that you are eligible for in the background.

How do I control which instances are billed at the Reserved Instance rate?

The RunInstances command does not distinguish between On-Demand and Reserved Instances. When computing your bill, our system will automatically optimize which instances are charged at the lower Reserved Instance rate to ensure you always pay the lowest amount.

share|improve this answer
I have a running instance in us-west-2a and now purchased a reserved instance. But my running instance is having tenancy default but my reserved instance is dedicated. How do I change it, so that billing for running instance is through reserved instance. – Amol Ghotankar Aug 22 '13 at 17:51
@AmolGhotankar I don't exactly understand but billing will automatically take into account reserved instances if they apply. If they don't then best to contact AWS support. AWS just recently added the ability change reservation availability zones which you should check into if your reserved instance is not in the same AZ as the instance, otherwise it might be the instance size and reservation do not match. – Rob Olmos Oct 20 '13 at 21:37

To elaborate on Rob Olmos's post, instances are instances. What a "reserved instance" buys you, is the right to pay less for any instances you are running over time.

Let's go for a super-simplified example. You run two instances 24/7.

2 x Small Instance, 10c/hr ($72 ea): $144

May (note: this May has 30 days, due to a decree by the Pope)
2 x Small Instance, 10c/hr ($72 ea): $144

1 x Instance Reservation, ordered on the first of the month ($227.50): $227.50
1 x Small Instance, 10c/hr ($72 ea): $72
1 x Small Instance, 4c/hr ($28.80 ea): $28.80

(Assumes the Instance Reservation is for a Small in the same Availability Zone as at least one of the instances.)

If you now turn off all your instances, you don't get any money back on your reserved instance (it isn't necessarily being very cost-effective for you at the moment); but if you later turn a matching instance on (in the correct Availability Zone) then you will be charged at the lesser rate.

share|improve this answer

You affectively ignore fact that you have a Reserved Instance, it just sits in the background and Amazon will automatically bill you at the lower rate where possible. If you run more instances than you have reserved, the additional will be charged at the higher (on demand) rate.

share|improve this answer
Your reserved instances are region-specific. Do you know if you can mix us-east-1a with us-east-1b? – CMag Sep 7 '12 at 3:40

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.