Spot Instances

If you have flexibility on when your application will run, you can bid on unused Amazon EC2 compute capacity, called Spot Instances, and lower your costs significantly. Set by Amazon EC2, the Spot price for these instances fluctuates periodically depending on the supply of and demand for Spot Instance capacity.

To use Spot Instances, you place a Spot Instance request (your bid) specifying the maximum price you are willing to pay per hour per instance. If the maximum price of your bid is greater than the current Spot price, your request is fulfilled and your instances run until you terminate them or the Spot price increases above your maximum price. Your instance can also be terminated when your bid price equals the market price, even when there is no increase in the market price. This can happen when demand for capacity rises, or when supply fluctuates.

You will often pay less per hour than your maximum bid price. The Spot price is adjusted periodically as requests come in and the available supply of instances changes. Everyone pays that same Spot price for that period regardless of whether their maximum bid price was higher, and you will never pay more than your hourly maximum bid price.