serverwentdown/alias

Does alias supposed to rewrite CNAMEs for external domains too?

Closed this issue · 5 comments

themisir commented

Let's say I have the following dns file:

example.org. 3600 IN CNAME twitter.org.

And I have alias and forward plugins enabled:

. {
  log
  forward . 1.1.1.1 1.0.0.1
}

example.org {
  file db.example.org
  alias
}

When I dig example.org, I see that DNS response contains both CNAME and A records (resolved from twitter.com). Is it possible to remove CNAME records and just respond resolved A records?

I'm new to CoreDNS stuff, so sorry if I misunderstood something.

serverwentdown commented

I'm not sure if there's something wrong with your configuration, but this is what I'm getting:

$ cat db.example.org
@	3600	IN	SOA	ns.icann.org. noc.dns.icann.org. 2019121376 7200 3600 1209600 3600
	3600	IN	NS	a.iana-servers.net.
example.org. 3600 IN CNAME twitter.org.
$ cat Corefile
. {
  log
  forward . 1.1.1.1 1.0.0.1
}
example.org {
  file db.example.org
  alias
}
$ dig @127.0.0.1 example.org
...
;; QUESTION SECTION:
;example.org.			IN	A

;; ANSWER SECTION:
example.org.		1800	IN	A	104.244.42.1
example.org.		1800	IN	A	104.244.42.65

;; AUTHORITY SECTION:
example.org.		3600	IN	NS	a.iana-servers.net.

;; Query time: 413 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Sun Mar 20 11:55:33 +08 2022
;; MSG SIZE  rcvd: 137
themisir commented

Ouch! Thanks for the reply. For a moment I thought maybe this plugin only supports CNAME aliases for internal names. Probably something is wrong with my config or coredns build.

themisir commented

Actually tried it again with a few more options. It looks like alias works with root domains but not with subdomains.

serverwentdown commented

Oh, it only works for root domains because subdomains don't really need to be aliased. I could add an option to make this plugin work for all requests, not just apex requests.

themisir commented

Oh, it only works for root domains because subdomains don't really need to be aliased. I could add an option to make this plugin work for all requests, not just apex requests.

Yeah that makes sense. No don't worry, I think my case is some edge-case, no need to modify current behavior. I ended up writing a small dns server to make sure it behaves as I expected. (I tried to modify this plugin to support that behavior but couldn't find a reliable way to do 😅)

Anyways, thanks for the replies!