Really basic sinatra web-app that reads the client ip, and as long as the api-key parameter matches the expected value, it fires off a request to update a cloudflare DNS record with that client ip address.

This has been working really well for me with the DD-WRT Custom DDNS Service setup & heroku. It probably breaks terribly if there's a proxy between the router and the web service.

heroku config must contain these env variables:

• CLOUDFLARE_ZONE, CLOUDFLARE_RECORD: The zone and record to update
• X-Auth-Email, X-Auth-Key: The Cloudflare authentication credentials
• LOCAL_API_KEY: A locally defined secret that incoming requests must contain in order to trigger a DNS update.

Here's an example of the DD-WRT setup: