Buying EC2 Reserved Instances with Boto

One of the great things about Amazon's EC2 service is the ability to scale up and scale down quickly. This elasticity really brings a whole new dimension to computing but one of the common criticisms on the forums early on was that if you didn't really need that elasticity, EC2 pricing seemed a bit high compared to some of the alternatives.

The new reserved instance feature in EC2 is a great way to save money on EC2 instances that you know you will be running most of the time. Basically, you pay some money up front and then get a much cheaper per-hour charge on that instance. If you leave a server up and running 24x7x365 the savings can be substantial.

Buying a reserved instance is a little strange. Rather than using an explicit transaction where you supply your credit card, etc. AWS chose to create a new API call in the EC2 service that purchases the reserved instance. For code monkeys like me, that's fine but some boto users were asking for a little wrapper around the process that would make the selection easier and reduce the risk of buying the wrong reservation.

So, I created a little Python script that guides you through the process and gives you the opportunity to review what you are about to buy and bail out if you make a mistake. At each step in the script, the available choices are presented to you in a simple command line menu. Once you make your choice, the script moves on to the next selection, etc. until all of the information is gathered.

The script is called buyreservation.py and it lives in the ec2 package of the boto library. It's included in the newest 1.7a release. To use the script, just "cd" to the boto/boto/ec2 directory and follow the prompts. A transcript of a session is shown below:

jobs:ec2 mitch$ python buyreservation.py
[1] RegionInfo:eu-west-1
[2] RegionInfo:us-east-1
EC2 Region [1-2]: 2
[1] m1.small
[2] m1.large
[3] m1.xlarge
[4] c1.medium
[5] c1.xlarge
Instance Type [1-5]: 1
[1] Zone:us-east-1a
[2] Zone:us-east-1b
[3] Zone:us-east-1c
EC2 Availability Zone [1-3]: 3
Number of Instances: 1

The following Reserved Instances Offerings are available:

ID=248e7b75-0799-4a55-a0cb-f8d28eb11921
Instance Type=m1.small
Zone=us-east-1c
Duration=94608000
Fixed Price=500.0
Usage Price=0.03
Description=Linux/UNIX
ID=4b2293b4-1e6c-4eb3-ab74-4493c0e57987
Instance Type=m1.small
Zone=us-east-1c
Duration=31536000
Fixed Price=325.0
Usage Price=0.03
Description=Linux/UNIX
[1] ReservedInstanceOffering:248e7b75-0799-4a55-a0cb-f8d28eb11921
[2] ReservedInstanceOffering:4b2293b4-1e6c-4eb3-ab74-4493c0e57987
Offering [1-2]: 2

You have chosen this offering:
ID=4b2293b4-1e6c-4eb3-ab74-4493c0e57987
Instance Type=m1.small
Zone=us-east-1c
Duration=31536000
Fixed Price=325.0
Usage Price=0.03
Description=Linux/UNIX
!!! You are about to purchase 1 of these offerings for a total of $325.00 !!!
Are you sure you want to do this? If so, enter YES:


If, at that point, you enter "YES" boto will go ahead and submit the API request to purchase the reserved instance(s), otherwise it will bail out. Hopefully the script provides enough guidance, handholding and confirmation to take some of the fear out of the process so go out there and save some money!