[londons_explore]

> runs out of every single instance type you have requested, terminates your Spot instances, and you can't launch any more On-Demand ones.

This is more common than you think.

Internally cloud providers schedule instance types on real hardware, and running out of an instance type likely means they have run out of capacity, and only a tiny amount exists in fragmentation. To access that tiny remainder, they'll terminate spot instances and migrate live users (which they have to do very slowly) to make space for a few more of whichever instance types make most business sense (which varies depending on the mix of real hardware and existing instance types).

It takes someone like AWS a good few weeks, sometimes months, to provision new actual hardware.

It isn't uncommon for big users to be told they'll be given a service credit if they'll move away from a capacity constrained zone.

[cm2187]

Is there a similar concept to airline upgrading? Better than to deny a paying customer to board the plane. Surely there must be spare capacity, somewhere in the datacentre, with slightly better specs.

[londons_explore]

Yes - they totally do that. If there is only space for a large instance, but you want a small one, they fit your small one in the free capacity, and there is now space for someone else to fit another small one next to it.

For business reasons they might decide not to do that though - your small instance might mean they have to say no to a big allocation later.

Instead they just delay your instance starting and hope other instances moving around opens up a more suitable location for it.

Theres an entire paper on the topic: https://dl.acm.org/doi/10.1145/2797211