private void invokeSetter(Object builder, String methodName, Object ... params) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
        // TODO: Does not work for native types.
        String key = methodCacheKey(builder, methodName, params);
        Method method = methodCache.get(key);
        if (method == null) {
            method = lookupSetter(builder, methodName, params);
            methodCache.put(key, method);
        }
        method.invoke(builder, params);
    }
This may run on both the config server and subscribing nodes.
We only have a urlDownloader set up when client side.
config/src/main/java/com/yahoo/vespa/config/ConfigPayloadApplier.java