public long size() {
            return hostnames().isEmpty() ?
                   Math.max(ipAddresses.addresses.stream().filter(IP::isV4).count(),
                            ipAddresses.addresses.stream().filter(IP::isV6).count()) :
                   hostnames().size();
        }
The number of hosts in this pool: each host has a name and/or one or two IP addresses.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/IP.java