We’re working on that problem at the moment.
For normal real-time tags, we simply enable history and set the Edge gateway up to do Tag History Sync with our central Ignition server.
Because we have unreliable 3G connections between Edge and Server, this is our preferred approach since it uses the store and forward engine. It also avoids constant polling between our Server and Edge, which is bad for our bandwith.
On our server we create expression tags that mimic the tags in Edge, and they run a script that gets the latest value out of the history provider on our Server.
The problem we’re having at the moment is for discrete data. For example somebody filling out a form on the Edge project and hitting save. We could push that through the historian approach, but retrieving a distinct dataset from the historian is proving to be a challenge.