private void noMoreAvailablePorts() {
        throw new RuntimeException
            ("Too many ports are reserved in Vespa's port range (" +
                    BASE_PORT  + ".." + (BASE_PORT+MAX_PORTS) + ") on " + hostname +
                    ". Move one or more services to another host, or outside this port range.");
    }
Reserves the desired port for the given service, or throws as exception if the port
is not available.

@param service the service that wishes to reserve the port.
@param port the port to be reserved.
config-model/src/main/java/com/yahoo/vespa/model/HostPorts.java