public int wantNetworkPort(int port, NetworkPortRequestor service, String suffix) {
        if (portDB.containsKey(port)) {
            int fallback = nextAvailableNetworkPort();
            NetworkPortRequestor s = portDB.get(port);
            deployLogger.log(Level.WARNING,
                service.getServiceName() +" cannot reserve port " + port + " on " +
                hostname + ": Already reserved for " + s.getServiceName() +
                ". Using default port range from " + fallback);
            return allocateNetworkPort(service, suffix);
        }
        return requireNetworkPort(port, service, suffix);
    }
Allocate a preferred port number for a service, fall back to using any dynamic port
config-model/src/main/java/com/yahoo/vespa/model/HostPorts.java