[Upstream DNS servers] wrong upstreams specification even when test passes

[jacktheripper19]

Prerequisites

Please answer the following questions for yourself before submitting an issue. YOU MAY DELETE THE PREREQUISITES SECTION.

• I am running the latest version
• I checked the documentation and found no answer
• I checked to make sure that this issue has not already been filed

Issue Details

• Version of AdGuard Home server:
  • v0.107.2
• How did you install AdGuard Home:
  • Docker
• How did you setup DNS configuration:
  • System
• CPU architecture:
  • AMD64
• Operating system and version:
  • Ubuntu 20.04.1

Expected Behavior

Setting up the upstream dns server using the hostname of the resolver should work

Actual Behavior

the test passes but the specification control returns an error HOSTNAME is not a valid IP

Additional Information

I have a setup where the upstream dns resolver unbound can change ip occasionally but it is on the same network as ADH, which means that it can be found using its hostname.
In the DNS settings, Upstream DNS servers, using [/local/]unbound:53 as an upstream server passes the test "Specified DNS servers are working correctly" but when applying the changes I get Error: control/dns_config | wrong upstreams specification: unbound is not a valid IP | 400

[ainar-g]

Hello and thank you for your report!

It seems like there are two issues here:

1. Using hostnames for plain DNS is currently not supported.

   @ameshkov, considering that we have bootstrap IP addresses, perhaps we could add a udp:// scheme support with hostnames?

2. The upstream test API should indeed validate the domain-specific upstreams as well. That looks like a bug.

[jacktheripper19]

Ok I see. In that case, do you have an idea of a good way to handle this kind of setup where upstream dns changes ip regularly ?

[ameshkov]

@jacktheripper19 would it be possible to use TLS on the unbound side? AGH currently will only resolve domain names for encrypted upstreams.

[ameshkov]

@ainar-g

@ameshkov, considering that we have bootstrap IP addresses, perhaps we could add a udp:// scheme support with hostnames?

Makes sense to me.

[EugeneOne1]

@jacktheripper19, we've just pushed the latest build to the edge channel. For the moment it should only invalidate upstream servers like the one in the issue. Could you please check if it properly reports the error and doesn't break testing of other upstream servers you have?

We'll also fill the separate feature request on support the udp:// schema since it needs modifying external libraries.

[EugeneOne1]

@jacktheripper19, I'll close the issue for now if you don't mind. See #4166 for the status of plain DNS hostnames support.