Mapping a remote serial port to a Debian VM

I have a Debian Stretch VM that is dynamically migrated between a few hosts. I need to connect a serial (RS-232) modem to it. Unfortunately, I cannot use the hypervisor for this.

I am looking for a reliable method of mapping a serial port from one (physical) server to a VM (in a serial-over-ethernet manner), but there's a requirement that this must provide a virtual device file (like /dev/ttySX) on the VM. Additionally, it'd be highly desired if the whole setup could re-establish the connection after rebooting either of the servers, without requiring manual intervention.