Berend, your points are very valid and close to the initial thoughts I had. When I laid out the observations I did realize, however, that the recent ELB failure did not per-se extend across AZs and that booting from EBS doesn't really add a new correlated point of failure. If you don't deploy across AZs for cost reasons then you have lowered your survival chances long ago before even talking about EBS. That's a business choice--valid in some cases, foolish in others. I'm surprised that you bring up the cross-AZ charges. Sure, I'd love for them to be lower or zero, but at the same time, I've not seen them as a dominating cost factor. By the time you decide to replicate you are accepting a bunch of 2x cost factors, if not more, and generally the cross-AZ traffic cost is low in comparison. Of course I'm sure there must be a counter-example out there. I do disagree with your statement that only Netflix manages to stay up. There are many other sites that do as well, they're just not so vocal about it. In the end it's a cost/benefit analysis, in the case of netflix the benefit of staying up is very high, so they can spend $$ on engineering that and they like to talk about it. Doesn't mean others are not doing good work too.