Tagged VLANs would be needed regardless, because I have only one server with one physical connection and I wanted to have processes on it on 2 different networks.

Docker is neither here nor there, you’re right it’s not needed for the solution. I was using it anyway, I know lots of selfhosters do, and it does make it easy to create an ipvlan and put an app on it.

Docker is not the only way to achieve containerization but I do appreciate and use containerization (and virtualization). It lets the host OS stay simpler and cleaner and prevents the various apps from messing with it. It makes it easy to control each app’s environment. You can do app containers, system containers or VMs as needed. It makes it easy to back up, restore and reproduce an app and its state, independently of the host OS or any other app.

Abstractions help… they empower you to do more. You invest some time into learning, sure, but it pays off later in time saved managing and the ability to do more complex stuff faster.

Troubleshooting is what it is. Nothing’s perfect, you’re going to end up troubleshooting something sometime not matter what you use.