isn't a simple out-of-the-box concept.
First things you have to ask yourself: How important is the info you serve and how much availability (uptime) is wanted. This can come with a very high price tag.
You mention a piece of webserver hardware that fails; What about a power failure, ISP failure, network failure etc etc? All of which can mean unwanted downtime.
I would advise you to search the web for linux failover
and get familiar with all possibilities that are available depending on your demands.