On Amazon EC2, will the Spot Instance price ever be higher than the On-Demand Price?

26
votes

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?

6
amazon-web-servicesamazon-ec2cloudinstances
A lot of people have had your thinking - and hence even those of us who just request a single instance manually might bid for spot instance, picking a ridiculous price, thinking that the savings will offset any extra paid on small and tiny spikes - in fact, costs have spiked up to 999$ per hour, and some spikes have lasted for pretty much a day - so beware! Those more involved have done calculations and found that 100% utilization of heavy reserved vs spot is about the same costs - so I just go with reserved. Let the game be played by those who have automated systems that switch to on-demand. – Cookie
This question appears to be off-topic because it is about Amazon's prcing system – user1864610

6 Answers

20
votes

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.

3
votes

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

2
votes

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?

2
votes

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.

1
votes

The point is that you have to bid "truthfully" (e.g., bidding according to your value). Please see here and there for more details

0
votes

I notice today that they have implemented a minimum pricing strategy - they're telling you 0.06 - but if you try to buy it - it will not launch for less than $1:

" Your Spot request price of 0.061 is lower than the minimum required Spot request fulfillment price of 1.0 "

... so much for all their "no minimum price" advertising and spot price documentation...