Re: default_file in subfolder

Sure.

{    "exposed" : true,    "rewrite_rules" : [        {            "source": "",            "target": "ui/index.html"        }    ]
}

In that case the URL does not change if you enter the root path of your application. But consider that you have to define further rewrite rules to hide the real structure in case you navigate to another files from that file.

Best Regards,

Florian