Mikrotik per-connection-classifier alternative in Linux iptables

You can do that combining iptables with ipset but I believe you would want to use nftables for this. With jhash and vmap and update you can do just that. A general example for creating cgnat with nftables can be seen at: https://github.com/diorgesl/php-cgnat

Would look at: https://wiki.nftables.org/wiki-nftables/index.php/Load_balancing

I am pretty sure that this: https://habr.com/ru/post/501234/

is what you were looking for.

I have also written an example for the usage of jhash with a 4/5-tuple based load balancing. You can simply change the jhash to calculate the hash with the srcip and then add it into a set or a flow table.