Yeah, what I mean is it's not just cloud costs vs. local hosting costs. You have to come up with different processes for SRE and IT (removing mundane hardware work, accounting for cloud idiosyncrasies), benchmark, make sure your hosting cloud can handle scaling up to some upper bound estimate of your future user base, etc. At a company the size of twitter these become legitimate concerns. I've been throttled on certain services of certain cloud providers at 600 data nodes lol... of course twitter can negotiate higher allowances but massive scaling doesn't happen with the flick of a switch, sometimes you need big, long-term, expensive contracts