Kamailio coupled with Asterisk are implemented in many huge installations.
The simplest way to set up load balancing is to use the dispatcher module.
The dispatcher.list file should be set up like:
# group sip addresses of your * units 1 sip:10.1.2.3:5060 1 sip:10.1.2.4:5060 1 sip:10.1.2.5:5060
the basic kamailio.cfg should be like:
loadmodule("dispatcher.so")
...
if ( method=="INVITE" ) {
# dst_select( "GROUP", "HASH METHOD")
ds_select_dst("1","4");
sl_send_reply("100","Trying");
forward();#uri:host, uri:port);
exit();
}
If you are interested in using the dispatcher to do 300 Redirect, you can do the following:
if ( method=="INVITE" ) {
dst_select_domain("1","4");
# you can also add prefixes, if you need to send account codes
# like:
# prefix("123456");
sl_send_reply("300","Redirect");
exit;
}
in this fashion, you can put in a very inexpensive Kamailio SIP server installation to use as a load-balancer for your * units.
Another option is to use SRV records for your asterisk server group and forward the message to the domain.