So, I have Ubuntu 18.04. I did not install any web server (as far as I know). All I want to do is to tell the web browser that when someone type my website like forosdeinmigracion.com, the URL box should show https://www.forosdeinmigracion.com.
Never mind. I just added the www to the domain in app.yml on DISCOURSE_HOSTNAME: www.mydomain.com and it worked. Now the site is directing to www.mydomain.com
I tried DNS but I guess the change was going to populate the net. I did use the app.yml to make it happen and I am happy with it. I am not planing to have other contents in my server.