[Serusers] Loadbalancing / high availability

[E. Versaevel]

Hello,

I was wondering if it is necessary for a SIP packet from a specific call to
always go through the same server?

For instance, if you have a load balancer distributing requests over a few
servers, it is possible that an INVITE ends up on 1 server while the
following INVITE with the credentials ends up on another, would this be a
problem (ie, break the authorization) or should you use a SIP aware
loadbalancer for this (who looks at the callid for example)?
Assuming the ser servers are setup to use the same userdatabase (and
t_replicate to eachother) the picture would be something like this:

			 |
		  --------------
	        |loadbalancer|
		  --------------
	             |
	             |
	    --------------------
	    |	       |         |
	-------   -------   -------
	|     |   |     |   |     |
	| ser1|   | ser2|   | ser3|
	|     |   |     |   |     |   
	-------   -------   -------

If you setup the servers with the same IP as the load balancer and stop them
from replying to ARP requests for that IP, replying back thru a NAT should
not be a problem.

Just thinking out loud, I could use SER for the load balancing and t_relay
the packets, however that would require some tampering with the VIA records
(and I should use a reply to via in that case to the original IP the SIP
request came from, eg not the load balancer) this way outgoing SIP traffic
would not have to go thru the ser loadbalancer again to get out, hmm, it
might even be possible to use a route-record header to get the packets back
at the correct server...


Kind regards,

E. Versaevel