On Wed, Aug 17, 2011 at 12:39 PM, Lars Ellenberg <[email protected]>wrote:
> On Tue, Aug 16, 2011 at 08:51:04AM -0600, Serge Dubrouski wrote: > > On Tue, Aug 16, 2011 at 8:44 AM, Dejan Muhamedagic <[email protected]> > wrote: > > > > > Hi Serge, > > > > > > On Fri, Aug 05, 2011 at 08:19:52AM -0600, Serge Dubrouski wrote: > > > > No interest? > > > > > > Probably not true :) It's just that recently I've been away for > > > a while and in between really swamped with my daily work. I'm > > > trying to catch up now, but it may take a while. > > > > > > In the meantime, I'd like to ask you about the motivation. DNS > > > already has a sort of redundancy built in through its > > > primary/secondary servers. > > > > > > > That redundancy doesn't work quite well. Yes you can have primary and > > secondary servers configured in resolv.conf but if primary is down > resolver > > waits till request times out for the primary server till it sends a > request > > to the secondary one. The dealy can be up to 30 seconds and impacts some > > applications pretty badly, This is standard behaviour for Linux, Solaris > for > > example works differently and isn't impacted by this issue. Works around > are > > having caching DNS server working locally or having primary DNS server > > highly available with using Pacemaker :-) > > > > Here is what man page for resolv.conf says: > > > > nameserver Name server IP address > > Internet address (in dot notation) of a name server that the > > resolver should query. Up to MAXNS (currently 3, see > > <resolv.h>) name servers may be listed, one per keyword. If > > there are multiple servers, the resolver library queries them in > > the order listed. If no nameserver entries are present, the > > default is to use the name server on the local machine. *(The > > algorithm used is to try a name server, and if the query times > > out, try the next, until out of name servers, then repeat trying > > all the name servers until a maximum number of retries are > > made.)* > > options timeout:2 attempts:5 rotate > Right, once can do this. But even with this it would take additional 10 seconds for requests sent to the server that's down before they timeout. In production environment that's absolutely unacceptable. > > but yes, it is still a valid use case to have a clustered primary name > server, > and possibly multiple backups. > And that's why I cerated this RA :-) > > -- > : Lars Ellenberg > : LINBIT | Your Way to High Availability > : DRBD/HA support and consulting http://www.linbit.com > > DRBD® and LINBIT® are registered trademarks of LINBIT, Austria. > _______________________________________________________ > Linux-HA-Dev: [email protected] > http://lists.linux-ha.org/mailman/listinfo/linux-ha-dev > Home Page: http://linux-ha.org/ > -- Serge Dubrouski.
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