Configuring Dynamic DNS Resolution in NGINX Open Source and NGINX Plus¶

This article explains the difference between static and dynamic DNS resolution in NGINX and how to configure dynamic DNS resolution.

NGINX resolves domain names when connecting to upstream servers, and the process differs depending on whether DNS resolution is static or dynamic.

Static DNS resolution¶

With static DNS resolution, NGINX looks up the IP address only once when it starts. If the DNS record changes, NGINX continues using the old IP until it is reloaded or restarted.

Example configuration using static DNS resolution:

location / {
        proxy_pass https://demo-app.com;
        include proxy_params;
    }

Dynamic DNS resolution¶

With dynamic DNS resolution, NGINX periodically re-resolves hostnames at runtime, so it detects IP changes automatically without needing a restart or reload.

Open-source NGINX availability

Dynamic DNS resolution is available in open-source NGINX since version 1.27.3.

To configure dynamic DNS resolution:

Add the resolve directive parameter to your upstream server directive, and use a resolvable hostname as your address:
```
server address [parameters] resolve;
```
Define the DNS server with the resolver directive:
```
resolver address [parameters];
```
Define the name and size of the shared memory zone using the zone directive. This keeps configuration and runtime state between worker processes:
```
zone name [size];
```
(Optional) Set the resolver timeout using the resolver_timeout directive:
```
resolver_timeout 10s;
```

Below is an example configuration for dynamic DNS resolution:

http {
    resolver 192.0.2.1 valid=30s;
    resolver_timeout 10s;
    upstream backend {
        zone backend 64k;
        server backend1.example.com resolve;
        server backend2.example.com resolve;
    }
    server {
        location / {
            proxy_pass http://backend;
        }
    }
}

Impact of dynamic DNS resolution on traffic processing

NGINX re‑resolves domain names when the DNS TTL expires. To instruct NGINX to ignore the TTL and re‑resolve names more often, add the valid parameter to the resolver directive, e.g.:

resolver 127.0.0.1 [::1]:5353 valid=30s;