And the nice thing about DO and some of their cohort is that they charge by the hour for servers. Fire up new droplets and install your upgrades on them, smoke test the system, swap your routing over to the new machines, back up the old droplets (just in case you missed something) and and then destroy them.

If that takes 4 hours you've hardly spent any money at all, and you're running your cluster the way a lot of people already do.