I got a task at my internship that sounded simple. Move one of our servers to a new AWS region, keep it the same as before, and spend as little money as possible.

That last part stuck with me. If you've spent any time reading about saving money on AWS, you've seen Spot instances everywhere. AWS says they can be up to 90% cheaper than normal on-demand instances. Ninety percent! I thought I'd found the easy win.

Then at standup, a teammate asked one question that killed the idea in about ten seconds:

"Where does this server keep its data?"

Here's what I learned, and the question I now ask before picking Spot for anything.

1. What a Spot Instance Actually Is

AWS has huge data centres full of servers, and not all of them are being used at any moment. Spot instances let you rent that spare capacity for a lot less money.

The catch is in the deal. AWS can take it back whenever it needs the capacity.…