private static ConfigKey<?> createConfigKeyFromInstance(Class<?> configInstClass, String configId) {
        String defName = ConfigInstance.getDefName(configInstClass);
        String defNamespace = ConfigInstance.getDefNamespace(configInstClass);
        return new ConfigKey<>(defName, configId, defNamespace);
    }
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