What are best options for dynamic dns for multi-WAN IPsec failover?

  • Since dynamic DNS is required for multi-WAN failover, what's the easiest/quickest/most reliable way to do so? We're not interested in putting our entire DNS out to a 3rd-party service. We're fine with our own servers for the most of it. But I can see some advantage in using a service just for dynamic DNS for a subdomain – or even a special-purpose domain --  just to handle the pfSense IPsec failover scheme.

    So for this limited use, who do people recommend?