My home network sits on a fast internet connection behind an Ubiquiti Networks EdgeRouter X but doesn't have the benefit of a static IP address. I've been meaning to set up a dynamic DNS entry for it for a while, but really wanted to make use of the fact I already manage my DNS with Cloudflare, which has a very capable API. Ubiquiti's EdgeOS has support for dynamic DNS by generating ddclient configurations and running them when the IP address changes, however the web GUI doesn't support everything that is possible with its ddclient version.

There are existing solutions to this problem, for example this support article easily found through a search engine. However, the solutions I've found are clunky hacks that will be missed by configuration backups, and therefore more confusing to reproduce in the future if necessary. I wanted something that would exist properly within the EdgeOS configuration system.

Through trial and error, I found there are only two small things preventing Cloudflare support from working, and both can be easily sidestepped.

1. The web GUI doesn't provide the cloudflare protocol in the drop-down. Using the EdgeOS configuration CLI allows this value to be specified manually.
2. The EdgeOS configuration schema doesn't allow for the zone setting required by the cloudflare protocol. Because ddclient configuration is basically a comma-separated list of option=value pairs, the setting can be injected as part of another setting, as long as the schema validation doesn't prevent it. The host-name setting currently allows it, e.g. home.example.com becomes zone=example.com,home.example.com.

Armed with this knowledge, the dynamic DNS client can be configured with the following commands:

configure
set service dns dynamic interface eth0 service custom-cloudflare login {{EMAIL}}
set service dns dynamic interface eth0 service custom-cloudflare password {{API_KEY}}
set service dns dynamic interface eth0 service custom-cloudflare protocol cloudflare
set service dns dynamic interface eth0 service custom-cloudflare server www.cloudflare.com
set service dns dynamic interface eth0 service custom-cloudflare host-name zone={{DNS_ZONE}},{{HOSTNAME}}
commit
save
exit

eth0

On my EdgeRouter X, eth0 is configured as the WAN link. Replace as appropriate on other setups, this should be the interface that will have your external public IP address.

{{EMAIL}}

The email address you use to login to Cloudflare.

{{API_KEY}}

Your Cloudflare "Global API Key", which you can get at https://www.cloudflare.com/a/account/my-account.

{{DNS_ZONE}}

The Cloudflare-managed domain that the desired DNS entry exists under, e.g. example.com.

{{HOSTNAME}}

The DNS entry that should be modified, e.g. home.example.com.