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NGINX Resolver Valid Flag | About

NGINX helps developers fine-tune various aspects of its behavior.
One such aspect is the resolver directive. It plays a key role in deciding how frequently NGINX resolves domain names.

Today, we are going to take a look at the “valid” flag within the resolver directive and how using variables for domain names can help with customization.

The valid flag in the resolver directive indicates the duration for which NGINX considers the answer from the resolver as valid and does not query the resolver during that period.

By setting a validity period, we can control how often NGINX recursively resolves the domain name, optimizing performance and minimizing unnecessary DNS queries.

For example:

Here, the resolver directive is set to 10.0.0.4 with a validity period of 30 seconds. This means that NGINX will re-resolve the domain name every 30 seconds, disregarding the Time-To-Live (TTL) provided by the DNS server.

Variable Usage for Dynamic Configuration

Using variables for the domain name in the proxy_pass directive enables dynamic customization of the resolution process.

In other words, when a variable is employed in proxy_pass, NGINX automatically re-resolves the domain name when the TTL expires, resulting in up-to-date information.

Here, NGINX dynamically resolves the domain name specified in the variable every 20 seconds. The resolver directive explicitly specifies the name server. Also, the valid parameter ensures NGINX re-resolves names at the specified frequency, ignoring TTL.

Handling Resolver Timeouts

To prevent potential delays, NGINX lets us set a resolver_timeout. This defines the maximum time it waits for a response from the resolver. If the resolver fails to answer within the specified timeout (e.g., 60 seconds), NGINX  handles the situation. Hence, avoiding prolonged wait times and potential errors.

With the valid flag in the resolver directive and using variables in domain names in the proxy_pass directive, we can optimize NGINX configuration.

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Conclusion

Today, our Support Engineers introduced us to the valid flag in the resolver directive in Nginx.