What Does the Resolver Param in Nginx Do?
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...
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
...
}
...
}
I followed this - and set /etc/resolv.conf value as the resolver value and it works fine. What is standing behind this?
2 Answers
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.
Nginx resolver directive is critical to any AWS environment that relies on ELB and proxy_pass. Here is the post that I wrote recently describing problem and solutions to the static DNS caching by opensource nginx:
Nginx resolver explained and how to deal with changing IPs
Basically it will boil down to following config for simple case:
server {
listen 80;
server_name example.com;
location / {
resolver 172.16.0.23;
set $upstream_endpoint
proxy_pass $upstream_endpoint$request_uri;
}
}
Elena Rostova holds a Master's degree in Public Health Journalism. She covers groundbreaking medical research, holistic wellness trends, mental health awareness, and nutritional science.
