private static boolean isConfigInstanceProducer(Class<?> clazz) {
        return clazz.getName().equals(ConfigInstance.Producer.class.getName());
    }
Compares the config instances and lists any differences that will require service restart.

@param from The previous config.
@param to The new config.
@return An object describing the difference.
config-model/src/main/java/com/yahoo/vespa/model/utils/internal/ReflectionUtil.java