Depends entirely on your business, but what I do is just tolerate the occasional 15-minute outage. There's increasing cost to getting more 9's on your uptime, and for me, engineering a system that has better uptime than Google Cloud does, by doing multi-cloud failover, is way out of favorable cost/benefit territory.
It is impossible to ensure 100% uptime, and it gets increasingly harder to approach that as you put more separate entities between yourself and the client. The thing is, you'll be blamed for problems that aren't in your control and aren't really related to your service, but to the customer. For example, local connectivity, phone data service, misbehaving DNS resolvers, packet mangling routers, mis-configured networks, mis-advertised network routes, etc. Every single one of those examples can happen before the customer traffic even gets to the internet, much less where you have your servers housed.
All you can do is accept that there will be problems that are attributed to your service, rightly so or not, and work to mitigate and reduce the possibility the problems you can, and learn it's not the end of the world.
