Yes, you can. But doing this is not "free", in that you are spending time doing this (potentially often) instead of an infinite number of other more productive things.
This alone isn't going to kill your productivity, but it's one of many of the annoyances of managing a large fleet using RIs. It's a cumulative burden, between figuring out reservations per-region, consider your baseline vs spot/on-demand levels, potentially put some other stuff you don't need on the RI market, and audit how many RIs in your inventory are actually in use.
This is an annoyance when you have a small fleet, but it quickly becomes an expensive nightmare when you start talking 100+ VMs. You start having to pay for expensive external tools to manage your expenses because this stuff sucks so much. Or write a ton of your own tooling (which is not free at all). Or just have someone who does this manually all the time (also really sucks).
This alone isn't going to kill your productivity, but it's one of many of the annoyances of managing a large fleet using RIs. It's a cumulative burden, between figuring out reservations per-region, consider your baseline vs spot/on-demand levels, potentially put some other stuff you don't need on the RI market, and audit how many RIs in your inventory are actually in use.
This is an annoyance when you have a small fleet, but it quickly becomes an expensive nightmare when you start talking 100+ VMs. You start having to pay for expensive external tools to manage your expenses because this stuff sucks so much. Or write a ton of your own tooling (which is not free at all). Or just have someone who does this manually all the time (also really sucks).