[dns-operations] Apex ALIASES that re NOT flattened CNAMEs

[Mark E. Jeftovic]

On 2024-10-23 1:38 AM, Peter Thomassen wrote:
> CAUTION: This email is from an external source. Be careful when 
> clicking links or opening attachments.
>
> Hi Mark,
>
> On 10/23/24 01:16, Mark E. Jeftovic wrote:
>> But most providers do it via CNAME flattening, so at the end of the 
>> process, they aren't really CNAMEs, they're A recs.
>>
>> But this will not work for Substack custom domains - and after going 
>> back and forth with their support, who took it up with some ops, it 
>> turns out that custom domains /at the apex/ on Substack will /only 
>> work/ when the query returns, literally, a CNAME when queried.
>
> Hm, so why is that?
>
> From Substack's web server perspective, the client is making an HTTP 
> request to their IP address, and it does not matter (in fact, the web 
> server does not know) whether that IP address is looked up from a 
> CNAME or via an A record directly. In the latter case, it also does 
> not matter whether that A record is maintained manually or 
> automatically (via CNAME flattening).
>

I believe it's because *target.substack-custom-domains.com* runs on 
Cloudflare CDN and they either need the custom domain to be /on 
Cloudflare/ nameservers or implemented the same way as Namecheap (which 
the original email email outlined).

Presumably if its the former, it's because CF can then use some internal 
mapping to know which custom domains are in use, for the latter, well, 
that's why I asked. It shouldn't make a difference, because the resolver 
should just re-query the CNAME target and wind up with A/AAAA recs 
anyway (right?)

After I sent the original message I realized that the example domain 
name Substack support gave me, doesn't even map to a custom domain 
there, it just redirects to main substack page, so now I'm wondering if 
perhaps I'm still not getting a totally accurate explanation from Substack.

- mark


-- 
Mark E. Jeftovic <markjr at easydns.com>
Co-founder & CEO easyDNS Technologies Inc.
+1-(416)-535-8672 ext 225

/"Never expect a thing you do not want,
and never desire a thing you do not expect."
-- Bob Proctor /
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