BIND9.2.0a2 Source Code

[Kevin Darcy]

Have you looked at the sdb mechanism in BIND 9 that allows you to use alternative
backends for your DNS data? I imagine you could also use it to store other stuff
alongside the DNS data, like metrics.


- Kevin

Vaishali Paithankar wrote:

> In fact, I wanted to do load balancing of the servers which are
> geographically distributed. In this case we need to have metrics which
> take into consideration the geographically distributed nature of the
> servers.
>
> Since, the DN System already has a distributed structure, this property of
> DN System can be used to make decision to choose the server.
>
> The DN Server would do the metric collection of e.g. RTT. This
> DN Server is assumed to be the nearest to the client to which
> the client has sent the query for I.P. address of the web site. So now,
> the client gets a good idea of the performance of all the servers
> depending upon client's geographical location .
>
> Instead of making changes in the zone files (RRs), is it possible to
> add/update the metrics in the memory where the zones are loaded (this was
> the reason to make changes in the source code) so that it not necessary to
> load the zones as and when we want to update the metrics ?
>
> Kevin and Brad, Thanks a lot for your advice/suggestions and for getting
> involved in the discussion.
>
> Vaishali
>
> On Thu, 19 Jul 2001, Kevin Darcy wrote:
>
> >
> > Vaishali Paithankar wrote:
> >
> > > Firstly, I am sorry for the repetative mails sent by me. This happened
> > > because my earlier mail to the list was bounced back. And I was trying
> > > to send it again.
> > >
> > > On Wed, 18 Jul 2001, Kevin Darcy wrote:
> > >
> > > >
> > > > This isn't just a BIND source code issue. You'd have to extend the protocol
> > > > so that the server would send this additional information in a form that the
> > > > clients would understand. And then you'd have to convince all of the server
> > > > and client implementors to adopt the protocol extension.
> > > >
> > > > Overall, you might be better off using a totally different protocol instead
> > > > of piggybacking on DNS. A Server Performance Metric Protocol or something
> > > > like that...
> > > >
> > > > About the best you can do _without_ protocol changes is to convince client
> > > > implementors to use SRV records, which send "preference" and
> > > > "weight" information to the clients so that they can make more intelligent
> > > > decisions about what server to use, and how to do failover. But SRV isn't
> > > > truly dynamic.
> > >
> > > To make it dynamic...
> > >
> > > How often a DNS loads its zones ?
> > >
> > > i.e. if we updated our SRV records frequently, DNS will also have to load
> > > its zones with the same frequency ?
> > >
> > > Or can't we load only SRV records or the information that has changed
> > > e.g. only the metrics in the SRV record ?
> >
> > With Dynamic Update, these questions become basically meaningless. The master
> > server gets the changes immediately. Now, how quickly the changes get out to all
> > of the slaves and to all of the caching servers in the world, is another question.
> > Most DNS-based load-balancer solutions "solve" this problem by using very small
> > TTL (time-to-live) values on their records. But that's an awful approach. It
> > wastes tons of nameserver resources and causes lookup latency. As Brad pointed
> > out, L4 load-balancing is a more technologically elegant approach, because from
> > the DNS perspective, the data stays constant. This fits DNS'es caching model
> > better.
> >
> >
> > - Kevin
> >
> > > If you want something dynamic, then you have to go to some
> > > > sort of load-balancing solution. If you look in the archives of this list for
> > > > the last few days, you'll see that we've been arguing about whether these
> > > > load-balancing solutions violate the DNS protocol and/or whether they are a
> > > > good idea or not.
> > > >
> > > >
> > > > - Kevin
> > > >
> >
> >
> > At 4:24 PM +0530 7/19/01, Vaishali Paithankar wrote:
> >
> >   i.e. if we updated our SRV records frequently, DNS will also have to
> > load
> > >  its zones with the same frequency ?
> >
> >         Yup.
> >
> > >  Or can't we load only SRV records or the information that has changed
> >   e.g. only the metrics in the SRV record ?
> >
> >          Nope.
> >
> >
> > >         This kind of thing does not belong in the DNS.  If you want to
> > do
> > load balancing, you should do it with mechanisms that do not involve
> > the DNS.
> >
> >         At the first level, you can put a Layer Four (L4) load-balancing
> > switch in front of the servers to be balanced, and the switch will
> > use any of several different methods (none of which depend on the
> > DNS) to determine which server is the "least loaded" and therefore
> > should be the one to handle a particular incoming connection.
> >
> >         See the archives of the load-balancing mailing list at
> > <http://www.vegan.net/lb/> for more information.
> >
> >
> >
> > > > Vaishali Paithankar wrote:
> > > >
> > > > > Hello,
> > > > >
> > > > > I have read about the concepts of DNS but am a new BIND user and
> > > > > just installed BIND9.2.0a2 on one of my Red Hat Linux 7 machines.
> > > > >
> > > > > I wish to try to incorporate some changes in BIND so that it returns
> > > > > metrics of Server (metrics like Server Load, RTT) with the I.P. Address of
> > > > > the Server.
> > > > >
> > > > > This is for the purpose of selection of "best" server by the Client.
> > > > >
> > > > > Which source code files should I go through / change to implement this ?
> > > > >
> > > > > Where can I find some help, documentation of structure of the source
> > > > > code of BIND ?
> > > > >
> > > > > Vaishali
> > > > > --
> > > >
> > > >
> > > >
> > > >
> > >
> > > --
> >
> >
> >
> >
>
> --