[thelist] DNS redundancy

Maximillian Schwanekamp lists at neptunewebworks.com
Mon Oct 4 22:14:59 CDT 2004


A Maynes wrote:

>I have just read this tip and would like like to know more about setting
>this type of backup procedure it soounds straightforward enough so if
>anyone could post a few links for this that would be great or a step by
>step guide?
>
Ken Schaefer wrote:

>And the DNS already has built-in redundancy - you can configure as
>many "name servers" as you want for each domain.
>  
>
True enough, but sometimes not implemented properly.  Most domains are 
configured with two nameservers, primary and secondary.  This alone 
should be enough redundancy, but in some situations the "redundancy" is 
in name only -- e.g. you're hosting sites on a single webserver which is 
also running DNS - with two IPs for *both* primary and secondary 
nameservers.  Or, in shared host situations, the hosting provider gives 
two nameservers for the domain, and too often these "two" are the same 
physical machine.  Ideally, the nameservers for a domain should be in 
two geographically disparate locations, but in practice -- especially in 
Small-Medium business and for freelancers using one server for client 
sites, even if they are two separate machines they're in the same 
datacenter, which could itself lose connectivity as a whole (e.g. 
hurricanes, electrical fires* ).  It generally takes 24-48 hours for new 
domain nameserver info to propagate across the internet, so in case of 
problems it's not really feasible to just update the domain.

If your site's hosting situation fits one of the descriptions above, you 
might use your own (or host-provided) nameservers *and* add as a third 
(tertiary) nameserver a backup DNS provider; you would gain the 
advantage of "real" redundancy (provided the backup is in a different 
datacenter!).  If your primary and secondary DNS server(s) go down, the 
tertiary would still respond to requests.  If your webserver goes down, 
you could update the DNS to route requests to a different IP entirely.  
This can happen almost in real-time in many cases - in fact, this is the 
operating principle behind "dynamic dns" used to host personal sites on 
home Cable/DSL connections with changeable IP addresses.  A quick Google 
search [0] will bring up some example providers of backup and dynamic 
DNS services.  Also, the registrar Enom.com (perhaps others) provide 
dynamic DNS services along with domain registration.

Obviously, the idea of backup DNS is most relevant in a commerce 
situation where even an hour of downtime is a serious problem with 
ramifications of lost sales and/or lost staff hours dealing with 
customer service/support issues arising from the outage.

* The impetus for this tip was a recent incident involving Alabanza, a 
hosting company providing the backend infrastructure for thousands of 
hosting [reseller] providers.  Alabanza had a fire [1] in their 
Baltimore datacenter, taking down approximately 200,000 sites, including 
my client's site.  The outage lasted for some 8 hours or so.  This is an 
extreme fubar, but outages of 1 hour are not so uncommon in the world of 
shared hosting. 

[0] http://www.google.com/search?q=backup+dns
[1] http://thewhir.com/marketwatch/ala092004.cfm


Maximillian Von Schwanekamp
Dynamic Websites and E-Commerce
NeptuneWebworks.com <http://www.neptunewebworks.com/>
voice: 541-302-1438
fax: 208-730-6504



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