[asterisk-users] is DNS SRV enough for failover?

[CunningPike]

This is so wrong it's not funny. The caching of DNS SRV records acts in
its favor when it comes to failover - the UAs already have the
information they need in their resolver cache to perform the failover
without having to make another DNS query.

The TTL you need to worry about is that of the SIP registration - UAs
will typically renew their SIP registration at the half-life of the TTL.
A short SIP registration TTL will permit devices which are not actively
placing calls to failover more quickly than they otherwise would. Of
course, a balance must be struck between short SIP registration TTLs,
and the amount of SIP registration traffic this generates. YMMV.

CP

On Tue, 2008-09-30 at 22:07 -0400, Alex Balashov wrote:
> Nhadie wrote:
> > hi,
> > 
> > i'm using DNS SRV for failover, i tried to test shutting the server 
> > down, sip client should still register on the other server but it did 
> > not.  i'm using x-lite which i don't know if it's doing a srv query. 
> > does this mean SRV is not enough for failover? if a client has dns 
> > caching would this cause a problem?
> 
> SRV records are DNS.  DNS is cached.  Ergo, SRV records are cached. 
> Ergo, if they are cached excessively - either because the TTL is long, 
> or in defiance of the TTL - it can cause a problem.
> 
> No, DNS is not a good way to do real-time failover for anything.
>