FTP to multiple servers using one domain without load balancing

Not sure what OS, etc. that's important. If it is Windows, here's what I've done in the past.

I'll just assume local user accounts:

1. set up the local user accounts on the computer for each "user/client"
2. In explorer setup the NTFS structure so that you have a "root" folder and inside that folder you have folders for each client/etc.
3. Set up the NTFS rights, so that each user (you can use a group called FTP users, and add them all to that group) has "List" rights to the root folder. Then give them specific rights to each of their "home" folders (read/write/whatever).
4. In IIS for the FTP site, create virtual directories named EXACTLY the same as the user accounts you created, and point each one to the right home folder. ie. virtual directory of BOBJONES points to d:\ftpsite\BOBJONES
5. go back into explorer and create a new folder in the same folder as the ROOT folder and call it DEADEND
6. give the FTP users list/read permissions to the DEADEND folder
7. Back in IIS set the "root folder" for the FTP site to the DEADEND folder

That's it.

now when BOBJONES logs into the FTP site he is in the BOBJONES directory. If he gets wily and tries to do a cd .. to go up to the parent/root he'll get knocked into the DEADEND folder and won't see the list of everyone else's home folders, etc. (NOTE: he can get back to his home folder by typing cd BOBJONES still)

ONE FINAL NOTE: anybody that has a user ID but no virtual directory named the same will get defaulted to the root directory which has been changed to DEADEND.

To load balance your servers you should consider both command and data channels. To load balance command channel I suggest you to use HAProxy. If you use it, you should specify in your /etc/haproxy/haproxy.cfg the following:

listen ftp-lb00
    bind IP:21
    mode tcp
    option tcplog
    balance leastconn
    server ftp-serv00 192.168.1.1:21 check
    server ftp-serv01 192.168.1.2:21 check

IP here is a public ip whereas the connection is then redirected to 192.168.1.0/24 network. You should also define NAT forwarding in your iptables. For instructions to do this you can look the accepted answer here (How can I port forward with iptables?).

To perform load balance of data channel you should run as root in terminal these commands

iptables -A POSTROUTING -s 192.168.1.1/32 -o eth1 -j SNAT --to-source IP
iptables -A POSTROUTING -s 192.168.1.2/32 -o eth1 -j SNAT --to-source IP

These settings are valid for so-called active data channel. For setup in passive data channel case and more detailed instructions, please, consult this article (https://gist.github.com/erkie/922996a2ec4125d79c7f8772cda328ce).