This image contains ddclient 3.8.3 on Alpine Linux 3.6. Based loosely on babim/docker-alp-ddclient. I use it to keep a CloudFlare domain updated (see CloudFlare's documentation).
To install as a service:
docker run --volume $(pwd)/ddclient.conf:/etc/ddclient/ddclient.conf --name ddclient --restart unless-stopped --detach -t mjenz/rpi-ddclient
Your config file should look something like this:
daemon=1800
foreground=yes
ssl=yes
use=web
web=dnspark
protocol=cloudflare, \
zone=(your zone), \
login=(your login), \
password=(your password) \
(your domain)