UCARP allows a couple of hosts to share common virtual IP addresses
in order to provide automatic failover. It is a portable userland
implementation of the secure and patent-free Common Address Redundancy
Protocol (CARP, OpenBSD's alternative to the VRRP).

Because UCARP does not require "promiscuous mode" on interfaces, it may be a
suitable option in environments where carp(4) may be difficult to deploy,
such as in clouds or other virtualized infrastructures.

WWW: https://github.com/jedisct1/UCarp