Alestic.com - A Personal AWS Blog by Eric Hammond

understand the commitment you are making to pay for the entire 1-3 years

Amazon just announced a change in the way that Reserved Instances are sold. Instead of selling the old Reserved Instance types:

• Light Utilization
• Medium Utilization
• Heavy Utilization

EC2 is now selling these new Reserved Instance types:

• No Upfront
• Partial Upfront
• All Upfront

Despite the fact that they are still called “Reserved Instances” and that there are three plans which sound like increasing commitment, the are not equivalent and do not map 1-1 old to new. In fact the new Reserved Instances are not even increasing commitment.

You should forget what you knew about Reserved Instances and read all the fine print before making any further Reserved Instance purchases.

One of the big differences between the old and the new is that you are always committing to spend the entire 1-3 years of cost even if you are not running a matching instance during part of that time. This text is buried in the fine print in a “**” footnote towards the bottom of the pricing page:

The new spot instances on EC2 are a great way to get some extra compute power at a price you can live with, especially if you are flexible on exactly when the instances run. On the other hand maybe you won’t get the compute power if the spot instance price never drops to the max price you are willing to pay.

The best way to approach auction type situations like this is often to simply list the maximum price you can afford. Your instance(s) will get run if and when the spot instance price reaches that price and you will regularly get charged less depending on what other users are bidding for their instances.

Though I don’t recommend trying to chase the spot instance price around, it is natural to be curious about what others have been paying and whether or not you might have a chance to get in with your bid.

The ec2-describe-spot-price-history command lists the historical values of the spot instance price for all sizes and types of instances. This is useful for studying fluctuations over time, but sometimes you’ll just want to know what the latest spot instance price is, even though this is not necessarily the price you would get charged if you opened new spot instance requests.

The following command shows the most recent spot instance price for each size of the Linux instances:

ec2-describe-spot-price-history -d Linux/UNIX |
  sort -rk3 |
  perl -ane 'print "$F[1]\t$F[3]\n" unless $seen{$F[3]}++' |
  sort -n

To check the spot price in a different region, simply add an option like

--region us-west-1

or

--region eu-west-1

As of the writing of this article, the prices returned for the us-east-1 region are as follows:

0.026	m1.small
0.05	c1.medium
0.11	m1.large
0.25	c1.xlarge
0.265	m1.xlarge
0.443	m2.2xlarge
0.997	m2.4xlarge

The exact spot instance prices will vary significantly from these samples over time and likely even during the course of a day. In fact, the spot instance price may occasionally exceed the on demand (standard) EC2 instance price.

Who’s going to be the first person to provide handy, real time, spot price history graphs by EC2 region, instance class (Linux/Windows), and instance type with correct X-axis date/time scaling?

Good luck bidding!