I don't think I've ever seen spotfleet not satisfy a request with all the same instance type. When the instance gets terminated, it seems to fill again with the same instance type as before (and then get killed again in busy periods).
For the past few weeks I've been having this exact problem with GPU instances, where on-demand requests would kill my spotfleet instances in the middle of a job, I'd spin up again, get killed again a few minutes later.
The only way to fix it without rewriting a bunch of stuff was to blacklist that instance type from my spotfleet requests.
It definitely wasted a bunch of my time though which seems to be increasingly more common with newer AWS APIs.
Fwiw, Product@SpotInst here. Might I suggest that you give us a try. We ward off against this specific scenario by calculating a Spot score based on Instance Type/AZ and deliver flexibility with a choice of different instance types.
For the past few weeks I've been having this exact problem with GPU instances, where on-demand requests would kill my spotfleet instances in the middle of a job, I'd spin up again, get killed again a few minutes later.
The only way to fix it without rewriting a bunch of stuff was to blacklist that instance type from my spotfleet requests.
It definitely wasted a bunch of my time though which seems to be increasingly more common with newer AWS APIs.