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Re: resolver does not work

Maxim Dounin
April 18, 2023 03:30PM
Hello!

On Tue, Apr 18, 2023 at 02:58:08PM +0200, mailinglist@unix-solution.de wrote:

> Hello,
> I have a nginx proxy in front of systemd-nspawn containers.
> The IP's of the containers are dynamic.
>
> When I start nginx *after* the  containers it works.
> When the IP of the container is changed while nginx is running i get a
> "Bad Gateway" error.
>
> The config looks like:
>
> server {
>     server_name foobar.example.com
> ...
>    location / {
>       resolver 127.0.0.53 valid=10s;
>       ...
>       proxy_pass http://container;
>    }
> }
>
> nginx is 1.1.18 so it should work as documented in
> http://nginx.org/en/docs/http/ngx_http_core_module.html#resolver
> The workaround there
> https://stackoverflow.com/questions/42720618/docker-nginx-stopped-emerg-11-host-not-found-in-upstream/52319161#52319161
> doesn't work.
>
> I have also try to config a upstream backend and the resolver in the
> server part or in the http part.
> The errors are: "upstream timed out" or "container could not be resolved
> (3: Host not found)"
>
> Whats wrong there?

The "resolver" directive is only used when the "proxy_pass"
directive contain variables, and therefore nginx isn't able to
determine upstream addresses when parsing configuration. Quoting
http://nginx.org/r/proxy_pass:

: Parameter value can contain variables. In this case, if an
: address is specified as a domain name, the name is searched among
: the described server groups, and, if not found, is determined
: using a resolver.

The "workaround", however, should work fine. Something like this
should be enough:

      resolver 127.0.0.53 valid=10s;
set $upstream "http://container";
      proxy_pass $upstream;

Note though that there should be an actual DNS name which can be
resolved with the DNS server configured with the "resolver"
directive. The "container could not be resolved (3: Host not
found)" error suggests that your DNS server does not return
anything for the name - you may want to dig further into systemd
to find out why it doesn't return anything.

--
Maxim Dounin
http://mdounin.ru/
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Subject Author Posted

resolver does not work

Anonymous User April 18, 2023 09:00AM

Re: resolver does not work

A. Schulze via nginx April 18, 2023 01:24PM

Re: resolver does not work

basti April 18, 2023 03:06PM

Re: resolver does not work

Maxim Dounin April 18, 2023 03:30PM

Re: resolver does not work

basti April 18, 2023 04:26PM

Re: resolver does not work

Maxim Dounin April 18, 2023 08:52PM

Re: resolver does not work

basti April 19, 2023 06:30AM

Re: resolver does not work

J Carter April 18, 2023 03:32PM



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