Ask HN: What would be the minimal non-SPoF web host?

Assuming you want to use your own hardware (no cloud computing), what would be the most simple, minimal way to continuously run a website (for instance just a simple HTML page) without any single point of failure ?

I guess using two physical machines in two different datacenters is a good start, but how do you handle automatically and instantly routing all requests to one if the other has failed?