[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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