Custom Domains - The Details In The DNS Settings

I've been helping people set up their custom domains for over a year now. We've dealt with simple setups, and complex setups - from a domain setup in 5 minutes using "Buy A Domain For Your Blog", to ones that take much longer because the domain itself is in use and requires Google Apps configuration. Occasionally, odd questions come up

Chuck, what is "3600"?

or

Does my blog have to be published to either "mydomain.com" or "www.mydomain.com"?

or

Do I have to point the blog to "ghs.google.com"?

The latter question wasn't easy to answer intelligently, basically I answered

You can point the DNS to any host name that you wish, but if you want a working custom domain, stick to "ghs.google.com", and lets get this done.

For an answer to the first two questions, and others, let's look at the setup process. Within the setup process, let's look at how this blog, "blogging.nitecruzr.net" is defined as a logical host in my domain, "nitecruzr.net".

If you're here looking for instructions on getting rid of the address entry for the recently decommissioned Google Apps server, see The GoDaddy Domain Manager: Removing An Address Entry.

You start with the GoDaddy Domain Manager, with the domain loaded. In this example, my domain is "nitecruzr.net". Once you're logged in, you do not re enter the domain name when you add an alias. Only enter the alias name, when prompted for "Alias".

Add One Virtual Host

blogging.nitecruzr.net. 3600 IN CNAME ghs.google.com.

Simply hit the "Add New CNAME Record" button, and you get the "CNAME (Alias)" applet.

• The Alias Name you enter as "blogging".
• The Host Name you enter as "ghs.google.com".
• TTL for .net domains defaults to 1 hour (3600 seconds).

Having successfully created the new CNAME record, we see it listed with the others.

• Host is "blogging".
• Points To is "ghs.google.com".
• TTL is 1 hour.

Add One Complete "SubDomain"

Some folks refer to this as a "subdomain", though it's actually 5 virtual hosts. This example shows an ASymmetrical DNS configuration.

nitecruzr.net.  3600 IN A 216.239.32.21
nitecruzr.net.  3600 IN A 216.239.34.21
nitecruzr.net.  3600 IN A 216.239.36.21
nitecruzr.net.  3600 IN A 216.239.38.21
www.nitecruzr.net. 3600 IN CNAME ghs.google.com.

Do you see the 3 "@" entries for IP addresses "64.233.179.121, 66.249.81.121, and 72.14.207.121", in the "A (Host)" section? That's the 3 Google Apps servers previously defined for the primary domain ("@"). If you were setting the domain up initially, you would hit the "Add New A Record" button 3 times 4 times, and enter the 3 servers (as of 2008/12, we have 4 Google Apps servers - the 3 are now offline), using "@" to designate the primary domain, each time. You would next add a "CNAME" for the "www" alias, pointing to "ghs.google.com", using "www" to designate the "www" alias.



Note: When you define the destination of "ghs.google.com", be aware of whether your DNS host is configured to accept "ghs.google.com" as an absolute or a relative address. This is an essential distinction, and may not be universal.

Now, let's examine a brief Dig log for the new alias, "blogging.nitecruzr.net".

;; QUESTION SECTION:
;blogging.nitecruzr.net. IN A

;; ANSWER SECTION:
blogging.nitecruzr.net. 3600 IN CNAME ghs.google.com.
ghs.google.com. 586847 IN CNAME ghs.l.google.com.
ghs.l.google.com. 203 IN A 72.14.207.121

blogging.nitecruzr.net. 3600 IN CNAME ghs.google.com. This was provided by my DNS server, after I entered it above.

• "blogging.nitecruzr.net." is the defined host name. The "." at the end makes it an absolute host name. You will always define an absolute host name.
• "3600" is the TTL, in seconds. "3600" specifies a TTL of 1 hour.
• "IN CNAME" is the syntax which defines a "CNAME" referral.
• "ghs.google.com." is the referred host name, again specified as an absolute address.

ghs.google.com. 586847 IN CNAME ghs.l.google.com. This was provided by "ghs.google.com".

• "ghs.google.com" is further referred to "ghs.l.google.com".

ghs.l.google.com. 203 IN A 72.14.207.121 This was provided by "ghs.l.google.com".

• "ghs.l.google.com" currently refers to the server at "72.14.207.121". "ghs.l.google.com" is a load balancing proxy server. If the server at "72.14.207.121" had been offline or busy, you would have a different IP address here. This is why we always use a "CNAME" referral to "ghs.google.com" for a proper custom domain definition.

When you define your alias, you only add the first of the 3 records above. The latter 2 are provided by the Google servers.

The URL of this blog is "blogging.nitecruzr.net". If the DNS server that services your computer requests the IP address of the blog, it will be told, by the DNS server that services the blog, to "ask the host ghs.google.com". After "ghs.google.com" has provided an IP address, that address will be retained ("cached") by your local DNS server for 1 hour.

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