[Asterisk-Users] Re: load balancing 20 asterisk servers

[Rich Adamson]

> Don't confuse load balacing with failover. They are quite different
> beasts and are handled differently. (sure, they can be "combined" into
> one solution, but they are still effectively very different)
> 
> Round Robin DNS based load balancing is still a viable load balancing
> solution (read some of the early Netscape white papers compaing round
> robin DNS to "intelligent" load balancers, the results were almost
> identical if not BETTER with round robin DNS.)

That's true for well behaved systems, but isn't true with the majority
of sip phones and adapters. The majority do not pay any attention to
the ttl fields in the dns response, and thus won't try another dns
query during follow on attempts. Plus, a fair number of phones and
adapters have problems with dns and the work around (as suggested by
the OEM) is to use hard coded IP addresses. There are actually far
more exception cases then there are solid sip devices (from a dns
perspective), therefore round robin with sip boxes will not see the
same results as the white paper you've referred to.

I have not tried to prove this, but I'd bet at least some money that
sip phones and adapters don't do a dns lookup each time a call is
placed. It _might_ do a lookup on each register, but not each call.

> As far as the failover part, all thats needed is a simple IP Address
> takeover. nowadays, ip address takeovers is VERY simple. change an ip
> address, possibly add a proxy arp, and clear the arp cache (or send a
> garp packet)

The OP was asking about load balancing 20 servers. IP address takeover
wouldn't apply nor would it scale. 
 
> I'm not necessarially saying this is or should be the solution for
> this specific problem, i havent really spent any time thinking about
> SIP. i'm just suggesting a possible easy solution, what people are
> saying, using SER to redirect to an asterisk server (thats the load
> balancing piece), and then simple IP Takeover for failover (why buy an
> expensive cisco box for doing something as easy as ARP)

That does sound like a very reasonable approach. :)