Apache runs on all hosts, on port 8080. It cannot run on the loopback adapter, because it has to be externally visible to the varnish instance which is running and listening on the floating IP. (However it is firewalled such that it is only accessible within the VLAN.)

The floating IP is implemented via ucarp, and when a host becomes the master pound and varnish are both started automatically. (They should be stopped when a machine loses the master-IP, but this is not currently done.)