[jlarky2012]

How fault-tolerant is your web server when datacenter has power outage? You can't build fault-tolerant system with one computing node by definition.

That means that if you planning to provide proper availability you want to work with system of applications, not just one. That means you should look into creating networking architecture that can handle all of that.

Most of the time it means that people just use tools that solve that for you, like load balancers. But it doesn't mean that somehow all modern applications are immune to failures.