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The spot prices are generally much less than the normal on-demand prices for EC2 servers but the prices also vary widely. Does it ever happen that the spot price is higher than an on-demand price?
If not, doesn't it make sense to always use spot instances with a max bid equal to that of the normal on-demand server? That way the spot instance will theoretically last forever (because the spot price will never cross the max bid) and will save you significant money. Does everybody already do this?
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Low, predictable prices You can purchase Spot Instances at prices up to 90% lower than On-Demand instances. Moreover, you can provision capacity across Spot, On-Demand, and RIs using EC2 Auto Scaling to optimize workload cost with performance.
A Spot Instance is an instance that uses spare EC2 capacity that is available for less than the On-Demand price. Because Spot Instances enable you to request unused EC2 instances at steep discounts, you can lower your Amazon EC2 costs significantly.
An AWS EC2 Spot Instance is an unused EC2 instance which is available for less than the On-Demand price. Spot instances are up to 90% cheaper than On-Demand instances, which can significantly reduce your EC2 costs. A Spot Price is the hourly rate for a Spot instance.
The following table displays the Spot price for each region and instance type (updated every 5 minutes). Spot Instances are available at a discount of up to 90% off compared to On-Demand pricing. To compare the current Spot prices against standard On-Demand rates, visit the Spot Instance Advisor.
Yes, the spot price can go over the on-demand price - for example, I just checked recent prices for an m1.xlarge image, which costs $0.68 / hour on demand, and the spot price spiked up to as much as $1.00 / hour.
When I was using spot instances heavily about a year ago, I found that it was possible to drive up the spot price by requesting multiple instances in one spot request. Effects like this made me decide that spot instances are definitely not a substitute for on-demand instances.
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Also note that you can't stop and restart EBS-backed spot instances, so if you only need the instance every now and then, you'll need to find other ways to have a persistent root store. See ec2-stop-instances
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I just watched a video here explaining the possible bidding strategies for spot instances: http://www.youtube.com/embed/WD9N73F3Fao?rel=0&hd=1
If I heard it correctly, the narrator claimed that some customer would switch from using spot instances to on demand instances when the price for spot instances goes above the on-demand instances.
The fact that spot instances would go above on-demand price would indicate to me that when this happens, it would not be possible to start on-demand instances since there would be no reason for Amazon to make on-demand instances available.
Has anybody tried starting on-demand instance when spot instance has a higher price and succeeded?
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Apparently yes: http://devblog.seomoz.org/2011/09/amazon-ec2-spot-request-volatility-hits-1000hour/
I’ve said before that we rely on AWS a lot, and today is no exception. However, we’ve been noticing quite a bit of pain the last week due to some extreme volatility in the spot price market. Normally, we use m1.xlarge instances, but over the last two days we’ve consistently lost machines in multiple availability zones due to the spot prices suddenly jumping to ridiculously high amounts.
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