Wackamole is an application that helps with making a cluster highly
available.

It manages a number of virtual IPs, that should be available to the
outside world at all times. Wackamole ensures that a single machine
within a cluster is listening on each virtual IP address that Wackamole
manages. If it discovers that any particular machine within the cluster
are not alive, it will almost immediately ensure that other machines
acquire their public IPs. At no time will more than one machine listen
on any virtual IP.

Wackamole also works toward achieving a balanced distribution of the
numbered IPs on the machine within the cluster it manages.