The problem is that actual high availability becomes too expensive for mere mortals. Even big dogs like Google, Netflix know there is a trade-off that can be wo

The problem is that actual high availability becomes too expensive for mere mortals. Even big dogs like Google, Netflix know there is a trade-off that can be worth it financially. The difference between five 9s, six 9s and seven 9s and beyond can be an order of magnitude more expensive at scale. Maintenance windows suck, but they work, and are predictable. It's easier to upgrade a database by bouncing it with a bit of predictable downtime, much much harder and expensive to do it live with zero downtime. Edit: not to mention that humans understand and are usually incredibly forgiving. But they are rarely forgiving when surprised with outages.