What does the Resolver param in nginx do?

nginx reverse-proxy resolver
guyyug picture guyyug · Oct 30, 2016 · Viewed 38.9k times · Source

I am using nginx as a reverse_proxy server with ELB. I am looking for explanation regarding the resolver value I set in the nginx.conf file. My nginx.conf:

http {  
   ...

   resolver x.x.x.x valid=30s;

   ...
}

server {

   ...

   set $elb "example.com";

location / { 
    ...

    rewrite ^/(.*) $1 break;
    proxy_pass http://$elb/$1?$args; 

    ...
   }
   ...    
}

I followed this - https://www.ruby-forum.com/topic/6816375#1166569 and set /etc/resolv.conf value as the resolver value and it works fine. What is standing behind this?

Answer

Dmitry MiksIr picture Dmitry MiksIr · Oct 30, 2016

The nginx resolver directive is required because the system resolver blocks. Nginx is a multiplexing server (many connections in one OS process), so each call of system resolver will stop processing all connections till the resolver answer is received. That's why Nginx implemented its own internal non-blocking resolver.

If your config file has static DNS names (not generated), and you do not care about track IP changes without nginx reload, you don't need nginx's resolver. In this case all DNS names will be resolved on startup.

Nginx's resolver should be used, if you want to resolve domain name in runtime without nginx reload.

Related questions

From inside of a Docker container, how do I connect to the localhost of the machine?

So I have a Nginx running inside a docker container, I have a mysql running on localhost, I want to connect to the MySql from within my Nginx. The MySql is running on localhost and not exposing a port to …

Read More
Nginx reverse proxy causing 504 Gateway Timeout

I am using Nginx as a reverse proxy that takes requests then does a proxy_pass to get the actual web application from the upstream server running on port 8001. If I go to mywebsite.com or do a wget, I …

Read More
How to serve all existing static files directly with NGINX, but proxy the rest to a backend server.

location / { proxy_set_header X-Real-IP $remote_addr; proxy_set_header Host $host; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; if (-f $request_filename) { access_log off; expires 30d; break; } if (!-f $request_filename) { proxy_pass http://127.0.0.1:8080; # backend server …

Read More