IT Tips and Tricks

Although the Linux Kernel has already a load-balancing feature, it doesn’t come without the price
of having to learn how to use it. Some tools like ‘LVS-KISS’ can help to do that job but still a bit too much
sometimes when one want just crude load-balancing without any fall-back features.
Here is a simple solution with iptables.
(Extracted from: http://www.thegeekstuff.com/2011/06/iptables-rules-examples/)

This uses the iptables nth extension. The following example load balances the HTTPS traffic to three different ip-address. For every 3th packet, it is load balanced to the appropriate server (using the counter 0).
iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT --to-destination 192.168.1.101:443
iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 1 -j DNAT --to-destination 192.168.1.102:443
iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 2 -j DNAT --to-destination 192.168.1.103:443

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Some extra related iptables use in that same area of interest:

Port Forwarding

The following example routes all traffic that comes to the port 442 to 22. This means that the incoming ssh connection can come from both port 22 and 422.
iptables -t nat -A PREROUTING -p tcp -d 192.168.102.37 --dport 422 -j DNAT --to 192.168.102.37:22
If you do the above, you also need to explicitly allow incoming connection on the port 422.
iptables -A INPUT -i eth0 -p tcp --dport 422 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 422 -m state --state ESTABLISHED -j ACCEPT