Regarding pub sub concept|OPC UA Standard|Forum|OPC Foundation

1. I have a source sensor at the edge that generates a xml-like payload every 9 seconds.rn2. I now want to use opcua-mqtt to deliver it across to the cloud opcua server.  This is what I did:rn2a. A opcua server A  is initialised and running.  A opcUA client is then started up to read the xml, processes it and updates the data to the opcua address space on the server.rn2b.  As the server nodes get updated, I use monitoreditems to write the data to a historian.  I also publish the same contents to a mqtt broker.rn3a.  Now I want to subscribe to the same content using a second opcua server B at the cloud side.rn3b.  After server b is started up, I use the callback function to read the contents off the mqtt broker, extracts the json contents and I want to update the address space of server b.rn3c.  However, in the callback function, I cannot access the server pointer.rn rn