I needed to start a new EC2 instance today and decided to try out the new spot instances, where you can reduce your instance cost by bidding on the maximum per-hour price you're prepared to pay. Since today's spot price was only 3.5c / hour, compared with 8.5c / hour for an on-demand instance, I was wondering: if I just bid a really high price, say 10c / hour, can I effectively be sure of getting a much cheaper long-running instance than an on-demand instance (since the spot instances are only charged by the current spot price) ?
I suppose it's theoretically possible for the spot price to go over the on-demand price, but as far as I can tell from the data on the AWS site, the spot price has always been well below that.
UPDATE: I've been monitoring the small instance spot price for a few weeks and it's been very consistent, only varying between 2.9c and 3.1c. I wrote up a more detailed blog post on spot instances, including a link to a Nagios plugin I built to monitor the spot price.
Best Answer
In theory, that's the idea, but don't host a webserver or anything on it that can't die. This is traditionally used for distributed jobs like data churning, rather than services, since if the spot price goes over your max bid, your server turns off.
Also, just making sure you have your numbers right, it's $0.085 per hour for on-demand, not $0.85. Might make a difference in your projections :)