Use Amazon EC2 spot instances

Recently Amazon introduced the ability to buy instance hours on a ‘spot’ market. Rather than try to describe the service myself, here is the description from the spot instances help page:

Spot Instances enable you to bid for unused Amazon EC2 capacity. Instances are charged the Spot Price, which fluctuates periodically depending on the supply and demand for Spot Instance capacity. To use Spot Instances, you place a Spot Instance request specifying the launch configuration for the instances, and the maximum price you are willing to pay per instance hour. If your maximum bid price is higher than the Spot Price, there is available supply, and your other conditions are met, Amazon EC2 launches instances on your behalf.

The maximum price you specify is not necessarily the price that you will pay. For example, if you specify $.50 as your maximum price and the Spot Price is $.30 for the period, you will pay only $.30. If the Spot Price increases, you will pay the new price (until it exceeds your maximum, at which time your instances will be terminated).

The spot price history is available the AWS Console and it seems the price for a small Linux instance rarely goes above 3 cents (vs a normal retail price of 8.5 cents). We been running an instance with a bid price of 4.5 cents for a couple of weeks and the actual cost has been $7.36 for 278 hours or 2.65 cents/hour – that’s better than a reserved instance. Likewise, Windows instances rarely obtain more than 6.5 cents so running with a bid price of 7 or 7.5 cents means you are gaining a healthy discount from the normal retail price.

So if you can tolerate that a machine might terminate abruptly (or you may pay something closer to the retail price) the EC2 spot prices are definitely worth a look.

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