May 222011

In The last article “Postfix Randomizing Outgoing IP Using TCP_TABLE And Perl“, i was writing about my experiment randomizing outbound ip. someone asked if the script can be mimicked as in the iptables statistic module. indeed, when using the previous script, the results obtained will really random. although that is what the script was created.

I found this wiki explaining about Weighted Round-Robin Scheduling.

Supposing that there is a server set S = {S0, S1, …, Sn-1};
W(Si) indicates the weight of Si;
i indicates the server selected last time, and i is initialized with -1;
cw is the current weight in scheduling, and cw is initialized with zero;
max(S) is the maximum weight of all the servers in S;
gcd(S) is the greatest common divisor of all server weights in S;

while (true) {
    i = (i + 1) mod n;
    if (i == 0) {
        cw = cw - gcd(S);
        if (cw <= 0) {
            cw = max(S);
            if (cw == 0)
            return NULL;
    if (W(Si) >= cw)
        return Si;

anyway, I do not have much time to implement that algorithm into the script, so I use an existing perl module List:: util:: WeightedRoundRobin
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