this is based on ovh-dyndns from Ambroisemaupate work.
https://docs.ovh.com/fr/domains/utilisation-dynhost/
Check every 5 minutes you WAN IP and if changed call OVH entry-point to update your DynDNS domain.
docker run -d --name="ovh-dyndns" \
    -e "HOST=mydynamicdomain.domain.com" \
    -e "LOGIN=mylogin" \
    -e "PASSWORD=mypassword" \
    ambroisemaupate/ovh-dyndns
version: "3"
services:
  crond:
    image: ambroisemaupate/ovh-dyndns
    environment:
      HOST: mydynamicdomain.domain.com
      LOGIN: mylogin
      PASSWORD: mypassword
    restart: always
By default, we use Google DNS to check your current DynDNS IP, but you can choose an
other DNS overriding NSSERVER env var:
docker run -d --name="ovh-dyndns" \
    -e "HOST=mydynamicdomain.domain.com" \
    -e "LOGIN=mylogin" \
    -e "PASSWORD=mypassword" \
    -e "NSSERVER=192.168.1.1" \
    ambroisemaupate/ovh-dyndns