AWS Spot Instances: Does the capacity-not-available Spot Bid Status Code mean no instances are available?

Question

I am writing code to track spot requests using the the documentation from this page: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-spot-instances-bid-status.html.

1. Is there any guarantee that if the capacity-not-available status code is returned, an increase to $10 per instance hour will occur for this instance, assuming that capacity continues to not be available (making it impossible to outbid because there are no more instances available)?

2. If question #1 is false, is it possible to receive this message while the spot price is at a reasonable price?

3. If question #2 is true, what are the cases where this can happen?

Answer 1

No, the price will not go to $10. It can, in fact, often be at the minimum spot price! For example, looking at the current spot price history for m5.24xlarge in us-west-2 at the moment I'm writing this answer, it's hovering around $1.32 (compared to the on-demand price of $4.61). However, bidding $4 on that instance type in that AZ gets either capacity-oversubscribed or capacity-not-available as the status.

One reason this can happen is because of recent changes to how spot prices change over time. In order to clear the spot market, the price might have to go up a bunch and terminate some instances with lower bids. However, because the price no longer spikes instantaneously, it can take a while for the price to catch up to where it needs to be to boot out the lower bids.

Answer 2

According to amazon's document

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-bid-status.html

If one or more request constraints are valid but can't be met yet, or if there is not enough capacity, the request goes into a holding state waiting for the constraints to be met.