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Tuesday, June 25, 2013

Custom Domain Instability Caused By Server Mismatch

A few blog owners become confused by the necessary configuration of the domain root, when setting up their custom domains.

Some blog owners, who do not have a good understanding of DNS principles, make mistakes when setting up the domain root (aka "naked" domain). From good intentions (trying to ensure that the domain performs better or differently), their naivete may actually make the domain perform worse - or not at all.

With more blog owners unable to buy a domain through Blogger, and forced to setup their own DNS addresses, this will become an common mistake, and an increasingly critical issue.

Blogger designed the custom domain feature to use "A" / "CNAME" referral, instead of DNS / frame forwarding.

The most obvious referral configuration - dual "CNAME" aka "symmetrical" DNS - is not supported by all registrars. Some registrars refuse to allow "CNAME" definition of the domain root, by policy.

Blogger provides an asymmetrical DNS complement and avoids dual "CNAME".

To make custom domain publishing more globally usable, Blogger provided an alternative to dual "CNAME" referral - a hybrid configuration which uses 4 x "A" referral, for the domain root. This configuration is also known as "asymmetrical" DNS.

Asymmetrical DNS uses 4 Google servers, accessed in a round robin sequence, to address the domain root.
mydomain.com.  3600 IN A 216.239.32.21
mydomain.com.  3600 IN A 216.239.34.21
mydomain.com.  3600 IN A 216.239.36.21
mydomain.com.  3600 IN A 216.239.38.21
www.mydomain.com. 3600 IN CNAME ghs.google.com.

Round robin DNS is pretty simple. Each server in the set is queried by the DNS client on the readers computer, in sequence, until one server responds. The first responding server is required to provide a suitable answer. If the first responding server provides an unsuitable answer, the DNS client has no alternative but to display yet another version of
Server Not Found
Error 404

We have 4 DNS servers to address the domain root, with quadruple redundancy.

Google uses the 4 servers to provide quadruple redundancy. During maintenance (with 1 server out of service, scheduled) - with triple redundancy - even two simultaneous emergencies (with 2 servers out of service, unscheduled) will not cause a total outage.

There is one weakness of round robin DNS. All servers, in the set, have to be equally capable of performing reliably. Well designed name server arrays will use identically setup computers, for the most predictable results.

A naive blog owner, including any additional or different server, in the set, risks having one server, responding to the round robin access - but providing an unsuitable answer.
mydomain.com.  3600 IN A 50.63.202.39
mydomain.com.  3600 IN A 216.239.32.21
mydomain.com.  3600 IN A 216.239.34.21
mydomain.com.  3600 IN A 216.239.36.21
mydomain.com.  3600 IN A 216.239.38.21
www.mydomain.com. 3600 IN CNAME ghs.google.com.

What is 50.63.202.39?
ip-50-63-202-39.ip.secureserver.net (50.63.202.39)

50.62.0.0 - 50.63.255.255
GoDaddy.com, LLC GO-DADDY-COM-LLC (NET-160-153-0-0-1) 160.153.0.0 - 160.153.255.255
GoDaddy uses forwarding - not referral - to direct traffic. Here, some (not all, and not always) prospective blog readers see
Server Not Found
Error 404

Some blog owners make a second mistake - which compounds the first mistake.
mydomain.com.  3600 IN A 50.63.202.39
mydomain.com.  3600 IN A 216.239.32.21
mydomain.com.  3600 IN A 216.239.34.21
mydomain.com.  3600 IN A 216.239.36.21
mydomain.com.  3600 IN A 216.239.38.21
www.mydomain.com. 3600 IN CNAME mydomain.com.
Here we see the "www" alias - which is what 95% of your direct traffic accesses - using the domain root for obtaining the address. Add to that the bogus server (in this example, "50.63.202.39"), and you will get a lot of complaints about sporadic connectivity problems.
Server Not Found
Error 404

The supported Asymmetrical DNS configuration is so simple, in concept.

This is so simple - if you only believe.
mydomain.com.  3600 IN A 216.239.32.21
mydomain.com.  3600 IN A 216.239.34.21
mydomain.com.  3600 IN A 216.239.36.21
mydomain.com.  3600 IN A 216.239.38.21
www.mydomain.com. 3600 IN CNAME ghs.google.com.
Though official instructions may disagree, my experience suggests that the domain root must be setup, properly, for a stable custom domain. There are but 3 proper DNS models, for a stable custom domain.

Please. The sanity which you save may be yours (or mine).

Dude, hit me with a comment!

Jodie Clarke said...

You really do explain things so well...thanks for sharing and also taking the time to help support others making these *ahem* silly mistakes ;)

Angelo's Blog said...

thanks for this, I was following blogger's instructions and my blog wasn't availabe ... once I removed the second CNAME as you suggested all is working fine now :)