Spot instances

AWS Spot Instances

There are two ways to start a computer on EC2: As a "persistent instance" or as a "spot instance". Persistent instances are guaranteed to remain active until you choose to terminate them, and for this you pay a fixed rate.

Spot instances, on the other hand, come from a pool of computers that all users bid for time on, and the price for using them is related to the number of people who currently want to use them. The spot instance price is normally substantially less per hour than the price of persistent instances, but during peak times (for example, if there's an event involving a lot of streaming video such as a popular sporting event or a national political debate, the hosting company may use a lot of spot instances, driving the per-hour price up for the duration of the event). To get a spot instance, you have to specify a maximum bid amount. For as long as this amount is less than the current market price, you will be charged the current market price per hour for each hour your instance is running. Spot instances take longer to start.

A summary of the pros and cons is:

                 | Persistent           | Spot
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Startup time:    | 3-5 minutes          | 3-20 minutes--variable
Cost:            | Fixed price per hour | Market rate--Usually cheaper except at times of high load
Remains online:  | At your command      | As long as market price is less than your maximum bid