The subdomain server.rocworks.at is redirected by my provider to my IP at home where Nginx (with Letsencrypt Certificate) is running and it forwards /grafana to my Grafana Docker Instance. Access to Grafana is possible via https://server.rocworks.at/grafana.

Nginx Configuration (sites-enabled/default)

server {
        listen 80 default_server;
        listen [::]:80 default_server;

        root /var/www/html;

        index index.html index.htm index.nginx-debian.html;

        server_name server.rocworks.at;

        location / {
                try_files $uri $uri/ =404;
        }

        location /grafana/ {
            proxy_pass http://docker1:3000/;
        }
}

Grafana Configuration (/etc/grafana/grafana.ini)

[server]
# Protocol (http or https)
protocol = http

# The http port to use
http_port = 3000

# The public facing domain name used to access grafana from a browser
domain = server.rocworks.at

# Root Url (NOTE: there is not Port in the URL)
root_url = %(protocol)s://%(domain)s/grafana

enforce_domain = false