Do you rent from AWS or some other provider? I wonder if there are issues with on-demand rent for those high-end GPU instances, is capacity always there or sometimes it is unavailable?
If there's some cost or availability question you have, AWS has some complicated bullshit to solve the problem for you. Check out reserved instances.
I don't touch AWS. We rent from an european provider. Demand can be tricky for serverless/spot-pricing. We have an always-on server so, no issues.