In his solution an Ignition Gateway in a private cloud will run some Perspective views, where some production data will be shown to his customer. My problem is:
production data are in the database which is connected to the Ignition in the Standard Site in the picture;
between the Standard Site and the private cloud there is a Gateway Network
Given that: how can Ignition in the private cloud get to the data? Is there any parameter that allow to share a database connection over a Gateway Network - something similar to the Remote Tag Provider. I was thinking of messaging to pass datasets as payload between the two gateways, but it is rather heavy, I think.
A remote tag provider, unless told otherwise, will forward historian queries to the source gateway over the GAN. For any other database operations, you will need to set up some other replication solution (database-specific, typically).
If you do set up DB replication, then your remote tag provider can be configured to divert historian queries to your cloud replica, which can help minimize your WAN traffic.
This is possible, but is not the most efficient, you're correct. We have considered implementing a first party DB query routing over the gateway network, but haven't decided exactly how it will work (and the security implications are a potential issue as well).
For now, messaging or DB replication as Phil mentioned are probably the way to go.
