I just started the container without any configuration and the UI does show up in the root / path. 

 yeah my problem was that I mounted the /app/public folder in the docker container to an empty ./public folder on the host filesystem. Removed the volume and now it works 

 when blossom-server starts it tries to serve the local "public" folder. it none exists then it will fallback to using the "public" folder that comes with the package
https://github.com/hzrd149/blossom-server/blob/master/src/index.ts#L65-L72

So if your seeing nothing at the root it might because you have a empty public folder 

 Ah, got it to work now, ty