The use case here is an AZ going down (reasonable to guard against) and an individual machine failure (the first reason we use HA like this anyway).
An AZ going down doesn’t make all other hardware reliable, and equally a machine going down from a cluster doesn’t mean that all AZs are going to be reliable.
Many products have uptime requirements above what Amazon can provide at the AZ or machine level.
An AZ going down doesn’t make all other hardware reliable, and equally a machine going down from a cluster doesn’t mean that all AZs are going to be reliable.
Many products have uptime requirements above what Amazon can provide at the AZ or machine level.