[SR-Users] load-balance to registered trunks?

[Alex Balashov]

On Sun, Sep 02, 2018 at 11:58:37PM +0100, David Villasmil wrote:

> I've got this scenario where some gateways will register on my
> kamailio and i need to send them calls on a load-balance fashion.  is
> this possible?

Sure, anything is possible in Kamailio if you write the logic for it.
:-)

I like stateless load-balancing methods where possible - the fewer
moving parts, the better.  

You can do a lookup() and then t_load_contacts(), 

   https://kamailio.org/docs/modules/5.1.x/modules/tm.html#tm.f.t_load_contacts

and examine the size of the `contacts_avp`, e.g. by iterating through it
with a while loop as you would any XAVP:

   $var(num_contacts) = 0;

   while(defined $xavp(whatever[$var(num_contacts)]))
      $var(num_contacts) = $var(num_contacts) + 1;

or you can reg_fetch_contacts() and do the same with the $ulc PV:

   https://kamailio.org/docs/modules/5.1.x/modules/registrar.html#registrar.f.reg_fetch_contacts

and access the number of registrants for the AOR via profile=>count:

   if(reg_fetch_contacts("location", "$ru", "blah")) {
       # Concurrent contact count is available as $ulc(blah=>count);

       ...
   }
 
I prefer the latter.

Either way, once you have a count, judicious use of cfgutils:$RANDOM

   https://www.kamailio.org/wiki/cookbooks/5.1.x/pseudovariables#random_-_random_number

will have you on your way to sending the call to a random contact of the
bunch. For sufficiently large samples, random distribution is
substantially similar to round-robin load balancing.

If you need failover with that load-balancing, you'll have to buffer
these contacts into an XAVP and serially fork through them with a
failure_route. Either way, it's all quite doable.

If what you're asking is whether there is a built-in facility to effect
load balancing across registrants, I'm not aware of one, though it could
be my ignorance.

-- Alex

-- 
Alex Balashov | Principal | Evariste Systems LLC

Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) 
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