Resolver not working as expected

[Steve Wilson]

On 27/08/2018 14:30, Maxim Dounin wrote:
> Hello!
> 
> On Mon, Aug 27, 2018 at 06:56:01PM +0530, Sharan J wrote:
> 
>> Hi,
>> 
>> Sample conf:
>> 
>>     http{
>>     resolver x.x.x.x;
>>     server {
>>     server_name _;
>>     location / {
>>     proxy_pass http://somedomain.com;
>>     }
>>     }
>> 
>> I have nameservers configured in my resolv.conf. But, somedomain.com 
>> will
>> be configured in x.x.x.x DNS server only. So, I have specified 
>> resolver in
>> my nginx.conf. However, during startup/reload I get "host not found in
>> upstream error". Why nginx is not considering resolver conf and 
>> searches
>> only in the nameservers configured in resolv.conf?
> 
> Names as written in the configuration are resolved while parsing
> the configuration using the system resolver.  DNS servers defined
> by the "resolver" directive are only used for dynamic / run-time
> name resolution - for example, when variables are used in the
> "proxy_pass" directive.

I didn't want to hijack this thread but my question seems relevant.

Is there a way to prevent dns resolution on a proxy_pass or upstream 
block during config parsing, or at least make it non-fatal?

background/reason: I've a backend server with dynamic IP which doesn't 
always resolve. It will resolve when it's expected to be working but may 
not be available at config parsing time.