Jupyterhub does not start kernels neither terminals

Question

I am trying to setup a jupyterhub with a nginx reverse-proxy within a docker container.

Here is my nginx configuration for jupytherhub:

location /jupyterhub {
            proxy_pass http://jupyterhub:8000/jupyterhub;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

            # websocket headers
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection $connection_upgrade;
            proxy_set_header X-Scheme $scheme;

            proxy_buffering off;
        }

And here is the config for jupyterhub:

c.JupyterHub.bind_url = 'http://0.0.0.0:8000'
c.JupyterHub.port = 8000
c.JupyterHub.base_url = '/jupyterhub'
c.JupyterHub.authenticator_class = "dummy"
c.Authenticator.admin_users = {'admin_user'}

However, it seems that the kernel does not start correctly: it keeps trying to connect, but does not manage. I can also manage to open a terminal within jupyterhub, but then the terminal is stuck, see the screenshot below:

terminal

It seems to be related to the websockets, but I am not sure. I checked the jupyterhub logs and I don't have any useful indication...

Many thanks!