vsftpd is relatively trivial to set up. It also supports FTP/S (FTP over TLS). That takes care of encryption in transit. It uses next to nothing for RAM while idle:
I was rather surprised Kopia doesn’t support FTP/S since SFTP (Secure File Transfer Protocol) is a bandwidth/CPU performance killer. It’s just too damn slow for serious consideration in deploying due to the protocol’s crypto overhead even on a 1 Gb symmetrical link with < 3.5 ms RTT/latency. I went with WebDAV over TLS instead. HTTP/WebDAV-enabled daemons use far more than 1 MB RAM idle:
That also assumes said daemons have full support for WebDAV-related RFCs (eg: Nginx does not without third party modules). Then I got my next surprise… which wasn’t quite so trivial:
In other words Kopia v0.19.0 is not suited for production deployment in conjunction with a WebDAV endpoint running on a forward-facing server. Put it behind your VPN at a minimum.
FileZilla Pro works for testing all three methods (SFTP, FTP/S, WebDAV (sas HTTP userhashes)). The F/OSS edition of FileZilla supports SFTP, FTP/S.
I would second this! The data is already encrypted, and I usually use Kopia over a VPN anyhow, which is also encrypted, so a third level of encryption seems kinda silly. However even if we do only want encrypted protocols, FTPS outperforms SFTP.
