There are probably not many people who would want to do this, but just in case you do, the information on how to let your Obihai device update Dynamic DNS can be found in this thread on the Obihai forum, posted by user giqcass, who writes:
Rough Draft for hackish DNS updates:
This hack will let your OBi update Dynamic DNS. It isn’t perfect but it works very well. It’s as simple as calling a url to update the DNS at afraid.org. I believe it would be a simple task to add this feature to the OBi firmware directly. So please add this OBiHai. Pretty please. Until then here you go.
Set up a Dynamic DNS host at http://freedns.afraid.org/
Go to the Dynamic DNS tab.
Copy the “direct” update url link.
Open your Obi admin page.
Click the System management page.
Click Auto Provisioning.
Under “ITSP Provisioning” Change the following.
Method = Periodically
Interval = This setting must be greater then 400 so not to over use resources. I use 3667.
ConfigURL = Paste the update link you got from afraid.org
Press Submit at the bottom of the page. Restart you OBi.
Remember that it’s okay to use more than one Dynamic DNS service simultaneously, in case you’re already using a different one that doesn’t provide you with a simple update URL.