If you have to have 5 9's starting with any cloud service is pretty tough sell at this point. You can build that type of system ontop of them. But it takes a

If you have to have 5 9's starting with any cloud service is pretty tough sell at this point. You can build that type of system ontop of them. But it takes a willingness to also build your own and use competing services adding even more complexity. The BYO or competing services bit is so you can keep the lights on even when the cloud eats it, not if. Part of 5 9's is planning for catastrophic failure. Things like 'what if the load balancer/router/backhaul/dns burns out, you have a spare on hand? Then what happens to services where you had them sticky?' Even then what if both the primary and secondary are out? What then? Lots of planning and making sure you know what to do when each of those cases happen. The nice bit though is many services can go down. Yeah it stings a bit (money, reputation, time, etc). But overall it is not that big of deal. But for the places where you can not go down. Tons of planning and tons of backup plans with backup plans, and a different style of producing code.