Having a hot spare, a database slave and a mirror of your assets so you can manually fail over? Probably a good idea. Architecting a very HA infra? Now wait and look hard at all the possible downtime causes (you have a DDoS provider for sure, Voxility or Cloudflare probably, what if they go down and so forth) and so and then look at what you are protecting against: a hardware failure which is exceedingly rare and again you can manually failover. The costs vs benefits will not come out in your favor up to a very large company size where even the smallest amount of downtime is so costly it doesn't matter how many engineering hours go into avoiding it.