Bad Hostname Error?

[Cabbar Duzayak]

On Wed, Dec 14, 2011 at 1:50 AM, Maxim Dounin <mdounin at mdounin.ru> wrote:
> Hello!
>
> On Wed, Dec 14, 2011 at 12:54:28AM +0200, Cabbar Duzayak wrote:
>
>> Hi everyone,
>>
>> Every once in a while, requests to my NGINX server are giving 500
>> errors as with bad hostname responses for http://:
>>
>> Can't connect to sub.mydomain.com:80 (Bad hostname: sub.mydomain.com)
>>
>> It turned out to be an issue with the DNS server, i.e. my ubuntu box
>> is failing to resolve this sub.mydomain.com address.
>>
>> What I don't understand is that why is NGINX making an ns lookup for
>> these requests??? Basically, when I make a request to this subdomain,
>> it should be resolving the request using the request header and proxy
>> it to localhost:81 or serving from local directory. And, I don't see
>> any reason to perform an nslookup here?
>
> The message you've provided suggests it's from your browser
> (proxy?), not from nginx.

It is actually a perl script on the same machine that is doing the
HTTP GET. And, the fact that it is giving a 500 error with an html
response made me think that it was NGINX that was replying, not the
browser / perl script ? But, I guess you are right... Thanks for
clarifying this.

>
>> My config file is as follows:
>>
>> server {
>>         listen   80;
>>         listen   [::]:80 default ipv6only=on; ## listen for ipv6
>>
>>         server_name  sub.mydomain.com;
>>         server_tokens off;
>>
>>         access_log  /var/log/nginx/access.log;
>>         error_log  /var/log/nginx/error.log info;
>>
>>         location / {
>>                 proxy_pass              http://localhost:81;
>>                 proxy_set_header        X-Real-IP $remote_addr;
>>                 proxy_set_header        X-Forwarded-For
>> $proxy_add_x_forwarded_for;
>>                 proxy_set_header        Host $http_host;
>>         }
>>
>>         location /html {
>>                 alias /home/user/html/
>>                 expires max;
>>         }
>> }
>>
>> DNS lookups will slow the server down, and trying to understand what
>> is going on here
>> Thanks...
>
> With such configuration nginx will only do a "localhost" name
> lookup once during configuration parsing.

Ah cool! So, there is no performance hit here.

Thanks a ton for the explanation.