bind round robin

[Chris H.]

Greetings all,
...
Quoting Doug Barton <dougb at freebsd.org>:

> Oliver Brandmueller wrote:
>>
>> DNS round robin is not about redundancy, the only thing you could have
>> that way is a kind of load balancing (not the most sophisticated way,
>> though). Whenever one of the servers fails, around half of the requests
>> still goes there and then times out/gets conn refused or whatever the
>> problem is. Prioritizing is not easily possible. Probably it helps if
>> you add one of the IPs more often to the set, but I never tried that and
>> did not read the docs on this topic, so before breaking your zone first
>> read the specs, if this works!
>
> Just replying to this bit first, in BIND it does not work to specify
> the same IP address multiple times for the same hostname. The server
> will collapse the duplicates into one unique entry when it reads the
> zone. I am not aware of any other authoritative name server for which
> this would work either.

While this /might/ hold true in some/certain situations. I /can/ say
after 3.5 yrs. of doing exactly this, that it does not collapse the
namespace into a single IP<-->name. Here is the excerpt from the zone
file(s) running a recent BIND version:

####################################################
#    hostA.domain.tld.zone
hostA          IN  A      XXX.XXX.XXX.XA
               IN  HINFO  IBM-PC/AT  UNICS/UNIX
               IN  MX 10  mx
               IN  MX 60  mx2
graphics       IN  A      XXX.XXX.XXX.XA
nameA          IN  A      XXX.XXX.XXX.XA
nameB          IN  A      XXX.XXX.XXX.XA
...
www            IN  A      XXX.XXX.XXX.XA
nameC          IN  CNAME  nameB
etc...

#    hostB.domain.tld.zone
hostB          IN  A      XXX.XXX.XXX.XB
               IN  HINFO  IBM-PC/AT  UNICS/UNIX
               IN  MX 10  mx
               IN  MX 60  mx2
nameD          IN  A      XXX.XXX.XXX.XB
graphics       IN  A      XXX.XXX.XXX.XB
hostE          IN  A      XXX.XXX.XXX.XB
etc...
#####################################################
Please note the RR (PTR) zone only lists RR's for
hostA and hostB. It is the responsibility of the hosts
own zones to delegate the hostnames for their own zones.
Both of these hosts are running Apache for the HTTPd
service, and both of them serve pages for graphics.domain.tld.

Now, on to your initial question...
Speaking of Apache; Apache has provided a solution for
the /exact/ situation you are enquiring about since v.1.2.
You will find it in the documentation that comes with the
installation. I will endevour to find it's whereabouts in
the doc's and provide a link. As I host those doc's. It
involves DNS and either the use of Perl, or http(s)d.conf
trickery. This, of course, all assumes that you are working
with Apache. :)

Best wishes,
Chris H.

>
> FYI,
>
> Doug
>
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FreeBSD 5.4-RELEASE-p12 (SMP - 900x2) Tue Mar 7 19:37:23 PST 2006
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