My flowfuse host is running on docker on a host with two NIC´s. NIC1 has internet acces, NIC2 is a secure network with no internet access. My plan is to use NIC 1 only to update the system and download nodes
to the palette. Viewing dashboards, programming and process data will be on NIC2.
Provided your system is setup correctly with routes directing IP addresses to the correct NIC then it will just work. node-red and npm do not need to know about the two NICs, the OS will sort it out.
Be aware though that as soon as you have one device that can contact both networks then you may well compromise the security of the 'secure' network. I am no expert in security, but I suspect anyone who is will tell you don't do this. The fact that you have to ask how to set it up suggests that you will not know how to keep the system safe.
What you want to attempt requires more than following a how to online. You will need to know how to test that it is secure after you configure a isolated NIC setup. Also you will need to know about issues with docker security if your running a containerized service and not on bare metal.
I rarely find documentation covering this issue when following a docker how to online.
Example of an oddity of Docker on linux and network isolation.