Custom domains, dns setup, what are the A records there for?

[Rob Curtis]

Hi,

We have a client that wants to use their sub-domain for one of our applications hosted on GAE.

Are the A records linked to the toplevel domain or are they linked to the subdomain?

For example, If I wanted to use:

foo.example.com as the domain, and example.com already points at some website, would the alias for the A records below all be set to foo or left blank (as it does when you add a new domain in GAE)?

Type	Data	Alias
A	216.239.32.21
A	216.239.34.21
A	216.239.36.21
A	216.239.38.21
AAAA	2001:4860:4802:32::15
AAAA	2001:4860:4802:34::15
AAAA	2001:4860:4802:36::15
AAAA	2001:4860:4802:38::15
CNAME	ghs.googlehosted.com	foo

Thanks

Rob

[George (Cloud Platform Support)]

The role of A type records consists in mapping a name to one or more IP addresses. The assumption here is that the IP address is known and stable. In your screen capture, the A record row always indicates an IP address under the Data column. The specific restriction is related to IP addresses, not subdomains. For related detail, you may have a look at the "Using subdomains" sub-chapter of the "Mapping Custom Domains" online document. 

[Rob Curtis]

Thanks George.

If I only intend to use the sub-domain of the domain, do we still need to add the A-records (because the cname record is pointing at ghs)?

(I don't full understand what the purpose is of the a records with blank alias).

Thanks

Rob 

On Wed, Jun 6, 2018 at 9:33 PM 'George (Cloud Platform Support)' via Google App Engine <google-a...@googlegroups.com> wrote:

The role of A type records consists in mapping a name to one or more IP addresses. The assumption here is that the IP address is known and stable. In your screen capture, the A record row always indicates an IP address under the Data column. The specific restriction is related to IP addresses, not subdomains. For related detail, you may have a look at the "Using subdomains" sub-chapter of the "Mapping Custom Domains" online document. 

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[George (Cloud Platform Support)]

DNS A-records are meant to be used in the configuration of root domains. A CNAME record is not allowed to coexist with any other data. If you use it for the www in www.somedomain.com, or for ghs, this coexistence is avoided, so your proposed usage above (pointing to ghs) is correct. You may check the RFC 1912 standard for more detail.