My "rivers" stopped updating two days ago, so I figured I'd have to log back in to my Amazon EC2 instance to get it going again.
I searched for Remote Desktop clients for the iPad, and found PocketCloud. The free version works fine -- I just had to enter the address for my EC2 instance and log in. Amazing that I can access Windows Server from my iPad! I just chose the Scan Now setting in the OPML Editor (not even sure that was necessary) to get my feeds updated.
I don't quite understand why the process of updating the json files discontinued, since I never stopped my instance from running. Hope I don't have to do this very often.