1. Obtain a CloudFlare API key if you haven't already.
  2. Create a DNS "A" record for the subdomain you intend to dynamically update.
  3. SSH into your EdgeOS device, and run the following:
configure
set service dns dynamic interface eth0 service custom-cloudflare host-name mysubdomain.mydomain.com
edit service dns dynamic interface eth0 service custom-cloudflare
set login [email protected]
set options zone=mydomain.com
set password myapikey
set protocol cloudflare
commit
save
exit
  1. Force an update by running update dns dynamic interface eth0
  2. If the update was successful, you should see something similar to the following:
interface    : eth0
ip address   : 123.123.123.123
host-name    : mysubdomain.mydomain.com
last update  : Sat Jan 25 11:20:37 2020
update-status: good