Depends on if those 9s are in series or in parallel. In series it multiplies to produce lower availability but in parallel they give you higher availability.
> AWS will use commercially reasonable efforts to make the Included Services each available for each AWS region with a Monthly Uptime Percentage of at least 99.99%, in each case during any monthly billing cycle....
So to achieve 99.99% within a region, every component should have at least 3 nodes and to better it deployment should go multi-region which will escalate the costs quickly.
Most application in reality don't even need four 9s so this works b beautifully for everyone. I work in outsourcing industry and in bad old days we had huge penalties and many rounds of explanations even for applications with no redundancy requirements ;).
But it's just Amazon credit nowadays and no one blinks and eye so it's win win the all.
So in that case you have to replicate across three regions to get 6 nines. So one component needs 9 copies running around the world to have 6 nines for the component.
