[VoiceOps] Load balancing

[John Todd]

On Nov 6, 2009, at 3:32 PM, Brian Sneddon wrote:

> None of those will preserve state, however, which I believe was the  
> main issue being presented by the original poster.  I use Linux-HA  
> quite a bit and it's great for service availability, but doesn't  
> really help if you're trying to perform a stateful failover.
>
> Brian
>

[snip]


I, for one, would be very interested to see anyone's results with the  
logically extreme version of "keeping state", meaning keeping media  
state.

Asterisk can't perform failover between two discreet systems and  
maintain media state, if media is indeed being handled as a B2BUA and  
RTP relay.  We (Digium) have been asked a few times about it, but the  
engineering effort is much much larger than the payoff and nobody from  
the open-source community has stepped forward with any code.  The  
amount of synchronization data that would have to be exchanged between  
two systems running RTP and signaling is large.  VERY large.  That's  
not to say it can't be done, but I just haven't seen it done even with  
VMWare or other VM-based systems which may claim to be able to  
synchronize instances between chassis platforms.

Most failures aren't hardware or chassis-based; they're software- 
based, so duplicating corrupted memory structures between two machines  
will give you (surprise!) two dead machines, or two dead apps on two  
machines regardless of the application being used.  So this has  
limited use.  Anyone who has code that relays minimal state WITHOUT  
mirroring the whole app/system so that two instances of (for instance)  
Asterisk could be synchronized without shared fate... I'll be very  
VERY interested in that.  :-)

So: has anyone out there done this with any RTP-capable systems  
running on Linux (Asterisk or otherwise)?  If so, can you post notes  
and operational techniques?


JT

---
John Todd                       email:jtodd at digium.com
Digium, Inc. | Asterisk Open Source Community Director
445 Jan Davis Drive NW -  Huntsville AL 35806  -   USA
direct: +1-256-428-6083         http://www.digium.com/