cloudflare-ddns is a little program that is really useful when you want to host something but your ISP only provides you a dynamic IP address. It uses Cloudflare's API to update a given DNS record when needed.
It's super fast and really lightweight, making it a valid choice for constrained environments.
This tool is a oneshot program: you run it, it updates the DNS record, and it terminates. To make it run periodically you could use a systemd timer or a cron job.
To run the tool you'll need an API token; cloudflare-ddns only needs the Zone.DNS edit permission.
Once you got the executable you can use it in two ways: you can pass the API Token and the record name as command line arguments or you can use a ini configuration file, tipically located in /etc/cloudflare-ddns/config.ini, by passing no arguments at all; here's the template. On custom installations the default config path might be different, but you can always locate it by running the tool without arguments. If you prefer, you can even use a configuration file in a custom location, using --config file-path.
If you're on Debian 12 or Ubuntu 22.10 the recommended install method is via the package manager; simply run apt install cloudflare-ddns and you'll automatically get the executable and a systemd timer. On other systems you can download the latest release from the GitHub Releases page, or, if you prefer, you can build the program yourself.
cloudflare-ddns is also a library! In fact, the command line tool is fully based on it. It is regularly tested with CI jobs, so you can be sure that it will always work as expected.
libcloudflare-ddns relies on libcurl only, while the executable also depends on inih.
To build the program, you'll need to install a C++ compiler and Meson; on Debian and derivatives you can do so with apt install g++ meson.
After installing the dependencies, you can build the program with meson setup build and then meson compile -C build. Meson will take care of downloading the necessary dependencies like libcurl.
If you're interested in only building the library, you can pass -Dexecutable=false to meson setup.
Here's an example of a systemd service + timer that periodically checks and eventually updates one DNS record
[Unit]
Description=Simple utility to dynamically change a DNS record
After=network-online.target
Requisite=network-online.target
[Service]
Type=oneshot
ExecStart=/usr/local/bin/cloudflare-ddns <api_key> <dns_record>
User=www-data
Group=www-data[Unit]
Description=Run cloudflare-ddns every 5 minutes
[Timer]
OnBootSec=1m
OnUnitActiveSec=5m
[Install]
WantedBy=timers.target