[Kamailio-Users] Redundancy and fault-tolerance

Alex Balashov abalashov at evaristesys.com
Tue Mar 3 22:12:41 CET 2009


Iñaki Baz Castillo wrote:
> El Martes, 3 de Marzo de 2009, Juha Heinanen escribió:
>> what i tried to say that if your two sip proxy host, which, for
>> performance reasons, should be physically close to each other, i.e., in
>> the same lan, see each other up and running, it does not mean that the
>> service is reachable from the outside.  you may have, for example,
>> some network equipment broken that affects reachability to one host and
>> not to the other.
> 
> You can create some OCF scripts that, in some way, test the connection from 
> outside. Not easy, but feasible.
> For example, such a script could log into an external machine via SSH and do a 
> PING or UDP test against the hosts.
> 

There are many ways to skin that cat.  I think Juha's point may be that 
Linux-HA doesn't natively provide an easy way to do this based on the 
assumption that it is a common use case / item of desiderata.

Personally, I would argue that it's just not that important.  If you 
lose outside reachability you've got other problems.  The types of 
failures Linux-HA looks to mitigate are related to physical node failure.

If the (LAN) network between the nodes gives out, Linux-HA has 
provisions called STONITH (Shoot The Other Node In The Head) to mitigate 
the cluster "split brain" problem/prevent the nodes believing that they 
are each the master and the other has failed.  It doesn't work perfectly 
(which, evidently, is something to which we are accustomed in the 
Kamailio community :-), but it works pretty well.

-- 
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
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