Base_url deprecation, but unclear what to do about it

Configuration
41

Where do you get the domain port?
and I guess 8123 as server_port ?

Edit:I was able to make it work. Look below if someone is still struggling.

default_config:
http:
  server_port: 8123
  #base_url: your_domain_name.duckdns.org
  ssl_certificate: /ssl/fullchain.pem
  ssl_key: /ssl/privkey.pem
  ip_ban_enabled: True
  login_attempts_threshold: 3
homeassistant:
  external_url: "https://your_domain_name.duckdns.org:8123"
  internal_url: "http://homeassistant.local:8123"