@af-pw I’ve reread your OP several times and its not clicking in my head to what the problem is.
I can tell you that its possible to have 2 standalone fog servers and have the images from server A replicated to server B using the fog UI. All of the images from server A can be replicated to server B and then server B can add its own images to its own server only. But there is a caveat with this solution and its not supported by the Developers. Let me explain.
For a fog “image” there are two components. The first is the raw data files stored in /images. The second is the data base record (meta data).
You can do this by on server A going into the storage nodes and add server B as a slave storage node. Then add server B to the storage group for storage A. This will start to replicate the images from FOG server A to FOG server B. If there are images you don’t want replicated to server B, on server A go into the image definition and disable replication for that image.
Now for the caveat. The process above will replicate the raw data to server B. What it will not do is copy over the meta data. You will have to do that manually. on FOG server A go into the image definitions and export them as csv. Edit the csv with your favorite editor removing image definitions you don’t want to appear on server B. Then on server B’s web ui import the image definitions from server A. This step really only needs to be done if/when you add new images to server A that you want to see on server B.