Nginx · December 19, 2023

Nginx Tip - Use the proxy_cache_revalidate directive for revalidation

Nginx Tip - Use the proxy_cache_revalidate directive for revalidation

Nginx is a popular web server and reverse proxy server that is known for its high performance, scalability, and flexibility. It is widely used by many websites and web applications to handle a large volume of concurrent connections and deliver content efficiently. One of the key features of Nginx is its caching mechanism, which can significantly improve the performance of websites by serving cached content instead of generating it dynamically for each request.

However, caching can sometimes lead to serving stale content if the cached data becomes outdated. To address this issue, Nginx provides the proxy_cache_revalidate directive, which allows you to control how often Nginx should revalidate the cached content with the origin server.

Understanding the proxy_cache_revalidate directive

The proxy_cache_revalidate directive is used to specify the conditions under which Nginx should revalidate the cached content. It takes a boolean value, which can be set to on or off. When set to on, Nginx will revalidate the cached content with the origin server based on the response headers received from the client.

By default, the proxy_cache_revalidate directive is set to off, which means that Nginx will not revalidate the cached content and will serve it directly from the cache until it expires. However, setting it to on can be useful in certain scenarios where you want to ensure that the cached content is always up to date.

Use cases for the proxy_cache_revalidate directive

There are several situations where using the proxy_cache_revalidate directive can be beneficial:

1. Dynamic content updates

If your website or web application frequently updates its content, you may want to enable the proxy_cache_revalidate directive to ensure that the latest content is always served to the users. By revalidating the cached content with the origin server, Nginx can determine if the content has been modified and serve the updated version if necessary.

2. Content expiration control

By enabling the proxy_cache_revalidate directive, you can have more control over when the cached content expires. Instead of relying solely on the expiration time set by the origin server, Nginx can revalidate the content periodically to check if it has been modified. This allows you to serve fresh content to the users even before the expiration time is reached.

3. Handling conditional requests

The proxy_cache_revalidate directive is particularly useful when dealing with conditional requests, such as those made with the If-Modified-Since or If-None-Match headers. By revalidating the cached content, Nginx can respond with a 304 Not Modified status code if the content has not changed, reducing the bandwidth usage and improving the overall performance.

Configuring the proxy_cache_revalidate directive

To enable the proxy_cache_revalidate directive, you need to add it to the Nginx configuration file within the http, server, or location context. Here's an example:

http {
    proxy_cache_path /path/to/cache levels=1:2 keys_zone=my_cache:10m max_size=10g inactive=60m;
    
    server {
        location / {
            proxy_cache my_cache;
            proxy_cache_revalidate on;
            proxy_pass http://backend;
        }
    }
}

In this example, the proxy_cache_revalidate directive is set to on within the location context. This means that Nginx will revalidate the cached content for requests matching this location.

Conclusion

The proxy_cache_revalidate directive is a powerful tool in Nginx that allows you to control how often the cached content should be revalidated with the origin server. By enabling this directive, you can ensure that your website or web application serves the latest content to the users, handle conditional requests efficiently, and have more control over the expiration of the cached content.

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