If you actually need so many 9's in the availability that it makes sense to invest in well tested robust failovers and resulting distributed-system application complexity (which most people don't test, they end up just paying for redundancy but getting maybe even reduced availability), you are in a very small minority and you will be highly skeptical of outsourcing this to a cloud vendor since their HA also goes tits up regularly. Witness how often cloud vendors have unexpected outages and read the post mortems.