how to force nginx to do DNS lookups

fancylad · 06-02-2011, 07:10 PM

Does anyone know if there is a way to get nginx to perform DNS lookups at regular intervals against hostnames that are defined for upstream servers? It seems nginx only performs a DNS lookup once, the first time it starts, and subsequently does not perform any other DNS lookups. This causes problems when the ip addresses of our upstream servers change.

I posted this same question in the nginx forum; however I also posted it here as it seems that not many of the posts there get answered.

http://forum.nginx.org/read.php?15,203481

bathory · 06-03-2011, 02:42 AM

Hi,

I guess you can use in nginx.conf

Code:

resolver x.x.x.x;

where x.x.x.x is the IP of a dns server that is aware of the changes in the upstream servers IPs.

Regards

fancylad · 06-03-2011, 10:43 AM

Thanks for the suggestion but I already tried that and it doesn't change the behavior. It only sets the nameserver nginx queries the first time it is started.

bathory · 06-05-2011, 03:47 AM

Yes, but according to Igor Sysoev (nginx author), cache should expire every 5 mins. See this post on the matter.
So unless upstream servers change ip addresses in less that 5 mins, you should not have a problem.

fancylad · 06-05-2011, 09:12 PM

Thanks. His post in your link does seem to suggest that the cache expires after 5 mins but that is definitely not the case.

bathory · 06-06-2011, 12:43 AM

Are you sure it's not the resolver you're using, that is not aware of the IP changes of the upstream servers?
You may install a lightweight resolver (like dnsmasq) locally and tune its cache to your liking

Regards

fancylad · 06-06-2011, 01:01 AM

Yes I'm 100 percent sure it's not the resolver. This is how nginx works, at least by default.