dns python and cnames

[hohmann22]

in DNS Python, is there a way to search for a given A record or ANAME and get all of its CNAMES assosiated with it? I know that I can search for a CNAME and get the Arecord with it associated with it.

for example, say I have a server that is called example.net and I have a jupyter server on it that is jupyter-example.net
and jupyter-example.net is a CNAME that points to example.net. Also, say I have an rstudio server on there that is
rstudio-example.net that also points to example.net. I know if I do something like
cnames = dns.resolver.resolve("jupyter-example.net", 'CNAME',search=True)
exmaple.net will be in the cnames variable but is there a way to do something like
cnames = dns.resolver.resolve(" example.net", 'CNAME',search=True)
and get it to return
jupyter-example.net and rstudio-example.net and whatever other cnames might be on it?
Thanks in advance.

[peterthomassen]

No, that's not possible. Also, it's not a restriction of dnspython; rather, this information is not available for lookup in the DNS.

[hohmann22]

Yeah, that is kind of what I thought, but I wanted to make sure.

[rthalley]

As Peter said, this is generally not possible in the DNS as anyone can CNAME anywhere, and the target of a CNAME is not informed. The general problem would involve searching the entirety of the DNS, and the DNS has no way of expressing or executing that kind of query.

It is, however, possible to use the DNS to store this information in certain situations. Like IP address forward and reverse mapping, if you control example.net and know that rstudio-example.net and jupyter-example.net point at example.net, you could add this to the example.net zone and then use the DNS to retrieve it.

$ORIGIN example.net.
aliases-for-example 300 IN PTR rstudio-example.net.
aliases-for-example 300 IN PTR jupyter-example.net.

Then a PTR query for aliases-for-example.example.net would return the information. Provided you only had a small number of these and kept them in sync yourself, this would allow some application to retrieve this info and use it. It's not clear how publishing this in the DNS would be a benefit over say putting it in a config file for the application, but maybe it's convenient to have all of the info in the example.net zone. I'm not sure what your ultimate purpose is, or if you control both sides, but I thought I'd mention this special case in case it met your needs.

[hohmann22]

If I did have control over example.net, how would I have python DNS query it for this information, thank you in advance.

[rthalley]

If you put "aliases-for-example" into the example.net zone like I suggested and keep it up-to-date, then

aliases = dns.resolver.resolve("aliases-for-example.example.net", "PTR")
for alias in aliases:
    print(alias.target)