(Roughly) based on https://github.com/alanszlosek/nodeftpd and https://github.com/billywhizz/nodeftpd
This piece of software provides a reverse proxy for FTP which can select the
target server based on the username. This is for example useful in a hosting
environment where you have many virtual servers but only a single IP address and
do not want to use different ports for different virtual servers. All other
reverse proxy servers I know either do not provide target server selection at
all or only based on some suffix ("@hostname") of the username. Furthermore,
ftpmult is an extremely simple piece of software (less than 300 lines) and can
thus be easily adapted to your needs.
See test.js for an example and adjust the callback getHostFromUsername to your
needs.