Effectively, it starts up cheap spot instances (based on specified criteria) across a variety of instance types to replace whatever regular instance in an autoscaling group comes online and then spins down the regular instance.
EG: That m4a you wanted may be expensive... but nobody is using m4ad so it's 85% off and it meets the specified CPU/RAM requirements... auto spotting will spin it up instead.
Having used it on and off over the years it is sometimes eyebrow raising to see 4xl boxes running cheaper than the xl box they replaced :)
It works, but it may depend on how resilient your workload is. We have timed spot instances that come online shortly before the top of the hour in the morning eastern, and via specifying instance alternates we'd often get instances that were much larger than our low-ish bids would warrant. Then most of them would get pre-empted <2 minutes later and there would be a bunch of churn as we had to replace them with what we should have gotten originally.
The author of AutoSpotting here, glad to see it mentioned in here and happy to help clarify such issues.
Are you sharing this as an experience of using AutoSpotting or other mechanisms to launch Spot instances?
What you described may still happen occasionally and it happened a lot with older versions, but the recent versions of AutoSpotting, especially the commercial edition available on the AWS Marketplace (although the community edition available on GitHub also does it to some degree) should avoid such situations in the default configuration should be much more reliable than before.
Actually when it comes to capacity, when Spot capacity is not available and we failover to on-demand, the latest AutoSpotting version will failover between multiple instance types with the same diversification used for Spot instances so you're pretty much guaranteed to have capacity even better than your initial single-instance ASG.
We also use the capacity-optimized-prioritized allocation strategy with a custom priority based on lowest cost, but also preferring recent instance types if available for more performance and lower carbon emissions.
Let me know if you have further questions about AutoSpotting, Im happy to help.
Effectively, it starts up cheap spot instances (based on specified criteria) across a variety of instance types to replace whatever regular instance in an autoscaling group comes online and then spins down the regular instance.
EG: That m4a you wanted may be expensive... but nobody is using m4ad so it's 85% off and it meets the specified CPU/RAM requirements... auto spotting will spin it up instead.
Having used it on and off over the years it is sometimes eyebrow raising to see 4xl boxes running cheaper than the xl box they replaced :)