private void portAlreadyReserved(NetworkPortRequestor service, int port) {
        NetworkPortRequestor otherService = portDB.get(port);
        int nextAvailablePort = nextAvailableBaseport(service.getPortCount());
        if (nextAvailablePort == 0) {
            noMoreAvailablePorts();
        }
        String msg = (service.getClass().equals(otherService.getClass()) && service.requiresWantedPort())
                ? "You must set port explicitly for all instances of this service type, except the first one. "
                : "";
        throw new IllegalArgumentException(service.getServiceName() + " cannot reserve port " + port +
                                           " on " + hostname + ": Already reserved for " + otherService.getServiceName() +
                                           ". " + msg + "Next available port is: " + nextAvailablePort + " ports used: " + portDB);
    }
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