Many corporate networks implement router redundancy for obvious reasons. Most of them are probably using very expensive hardware with proprietary protocols, but in fact it is possible to build such a setup for less than EUR100 and use it at home. Just get a couple of cheap routers that are well supported by LEDE/OpenWrt.

In part 1 I went over the basics of failover. The problem with such a setup is that TCP connections will not survive a failover from ar0 to ar1, or vice versa. The main issue is that both routers have a different WAN IP, and in this case, seamless failover will never work.