@rimelek Thank you for your reply.
To answer your first question mentioned here:
Just because not everyone knows JupyterHub, let’s clarify that when you write “host container” you mean the JupyterHub container which will start new containers for each user when they log in on the web ui served by the JupyterHub container. Right?
Yes, you are right.
Why do you expect to see that directory?
Maybe I misunderstood what I read about volumes. I also read here in this post that it was possible to share a directory between containers but I was not sure how to apply the implementation they mentioned to my current deployment.
Thank you for your suggestion to use a REST API or S3 storage. I will look that up, but it would be better if it is possible to do it with the approach I mentioned.
Thanks again for your reply. if you have any idea about what they mentioned in the post I linked (and time to check it out 
), it would be great.