Your Blog, Custom Domains, And The Quadruplet Google Apps Servers

Some people can't see the forest, for the trees. Occasionally, we see a query from a perplexed blog owner, seeking to publish to a custom domain.

Google wants us to repeat the same IP address 4 times?

216.239.32.21
216.239.34.21
216.239.36.21
216.239.38.21

Uh, aren't they're the same? Why the needless duplication?

Like quadruplets (newly born human children), you may need name tags to distinguish one server from the other. But, if you look closely enough, no, they aren't the same. As always, I'll present these examples using excerpted Dig logs.

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.

"ghs.google.com" is a DNS server array, with multiple levels and multiple redundant parts. We use "ghs.google.com" to resolve the "www" alias of the domains, using "CNAME" referral. Most custom domains are published to the "www" alias - so "ghs.google.com" is massively robust, with redundant parts.

If we use a similar "CNAME" referral to resolve the domain root, aka the "naked domain", we could interfere with resolution of email, FTP, and other possible auxiliary domain services hosted, by the registrar. Instead, we use multiple "A" referrals, mutually redundant.

Long ago, until November 2008, we used "64.233.179.121", "66.249.81.121", and "72.14.207.121", which were triple mutually redundant equivalents of "ghs.google.com". And, you could easily see "64.233.179.121", "66.249.81.121", and "72.14.207.121" as different IP addresses.

mydomain.com. 3600 IN A 64.233.179.121
mydomain.com. 3600 IN A 66.249.81.121
mydomain.com. 3600 IN A 72.14.207.121
www.mydomain.com. 3600 IN CNAME ghs.google.com.

Now, we use the quadruple mutually redundant configuration. And, "216.239.32.21", "216.239.34.21", "216.239.36.21", and "216.239.38.21" are different IP addresses, though they look the same - if you don't look closely enough.

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.

So, why four servers? Won't one do? Preferably, yes. But not one server is going to be 100% reliable, or last forever. Every computer ever made, like every human born, will die, one day. Your blog (and your domain) depends upon DNS, to resolve its address. If you specify one server, and that one server goes down, your domain will be out of service - to the people depending upon that one server.

As I wrote above, "ghs.google.com" is a redundant server array. But we have to use a "CNAME" to reference "ghs.google.com" - and we can't always use a "CNAME".

www.mydomain.com. 3600 IN CNAME ghs.google.com.

When we have to use an "A" referral to resolve the domain root, we can't use a name, such as "ghs.google.com" - we have to use an IP address. Google provides four mutually redundant individual servers, each responding to a specific IP address, for custom domain clients to access in a round robin sequence.

If any one server in the array becomes overloaded or goes out of service, and doesn't respond to a DNS query, the DNS resolver, on any client computer, will try the next server defined - if there is another server provided. If your domain provides just one server to resolve its address, and that one server goes down, your domain goes out of service. Your readers will see, yet again

404 Server Not Found

But wait - - there's more. Since Google provides four servers, and only one is out of service, they won't regard that as a major emergency. They still have three servers online - and nobody is losing sleep. Except, of course, you.

Google will repair or replace their one down server, when it is convenient to them. Maybe that will be next week, when their DNS server technician gets back from vacation.

Is that not convenient to you? Sorry.

With an asymmetrical configuration, you may not publish to the domain root. Your only valid choice is to publish to "www.mydomain.com", and select "Redirect mydomain.com to www.mydomain.com". If you publish to "mydomain.com", you will eventually see

Another blog is already hosted at this address.

or

Blogs may not be hosted at naked domains.

If you want to publish your blog to a custom domain using an ASymmetrical configuration, always publish to "www.mydomain.com", not to "mydomain.com". If you want to publish to "mydomain.com", you'll have to use a Symmetrical DNS configuration, and risk losing services hosted by your registrar. If you go with the first option, you will need all 4 servers - if you want a reliable and supported custom domain.

If your registrar or hosting service does not support 4 x "A" DNS addresses setup, you may want to use a (free) third party DNS host. Now, here's hoping that your registrar allows easy configuration of third party DNS service.

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