public final String getConfigId() {
        if (configId == null) throw new IllegalStateException("The system topology must be frozen first.");
        return configId;
    }
ConfigProducers that must have a special config id should use
setConfigId() instead of overloading this method.  This is
because config IDs must be registered through setConfigId().
config-model/src/main/java/com/yahoo/config/model/producer/AnyConfigProducer.java