Surely there is a better way to do that, but this method has worked for me correctly. I take this message to ask developers to add a button for the automatic generation of let'sencrypt SSL certificates, specific for the ispConfig control panel in Tools or System. In my example I assume that the ispConfig server has an FQDN name with subdomain: isp.example.org After entering ispConfig at https://isp.example.org:8080 and accepting the risk that firefox or chrome warns when entering, I have created a subdomain with isp.example.org with SSL and Let's Encrypt. From the console by ssh # cd /usr/local/ispconfig/interface/ssl # mkdir stop # mv ispserver.* stop # ln -s /etc/letsencrypt/live/isp.example.org/chain.pem ispserver.crs # ln -s /etc/letsencrypt/live/isp.example.org/fullchain.pem ispserver.crt # ln -s /etc/letsencrypt/live/isp.example.org/privkey.pem ispserver.key # reboot You may not need to restart the server and it is sufficient to restart apache with: # service apache2 restart But since I had to reboot anyway for a kernel update, I did the reboot. Now, Google searches for an "ssl checker" and check that your server at 8080 port, has a valid Let'sEncrypt ssl, inserting in the form "isp.example.org:8080" The test must be OK. Now you can enter with your browser in the control panel at https://isp.example.org:8080 Note that it is possible for your browser still warn about the wrong certificate. If this happens, clear the browser cache or use another one for now.