Port management in a horizontally scaled file transfer system

An example method of file transfer between a client and a server includes: initiating, by the client, a front-end control connection between the client and a horizontally scaled proxy service; creating, by a first proxy instance of a plurality of proxy instances of the horizontally scaled proxy service, a back-end control connection between the first proxy instance and the server; returning, to the client from the first proxy instance, a unique client parameter associated with the front-end connection as a destination port for a front-end data connection; initiating, by the client, the front-end data connection between the client and the horizontally scaled proxy service, the front-end data connection using the destination port as returned by the first proxy instance; and creating, by the first proxy instance, a back-end data connection between the first proxy instance and the server.