load-balancing in DNS using two A records

Sam Wilson Sam.Wilson at ed.ac.uk
Wed Dec 21 10:41:31 UTC 2011

In article <mailman.581.1324405362.68562.bind-users at lists.isc.org>,
 Matus UHLAR - fantomas <uhlar at fantomas.sk> wrote:

> On 20.12.11 19:37, Martin T wrote:
> >I have seen setups where one domain name has two address records.
> >First IP address is in the ISP-A network and the other one is in the
> >ISP-B network. In case I execute "host www.<domainname>.com", I always
> >get two IP addresses as a reply and they always appear by turns. Am I
> >correct, that setup like this provides redundancy as well as
> >load-balancing?
> Kind of. It's much better to have real load-balancing and vailover by 
> multiple links or L3 load balancers. 

If you're really cheapskate and have a little scripting expertise you 
can do what we did before we went to hardware load balancing.  Give your 
systems names with short TTLs in a dynamic zone.  Have a watchdog 
process monitor the systems and remove any that don't respond.  It's not 
generally fast enough to help individual clients but it can help the 
overall availability of a system.  It's victim to browsers ignoring 
TTLs, of course, though I've never been able to verify such browser 
behaviour myself.


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