Nginx Tip - Use the fastcgi_cache_bypass directive for conditional FastCGI caching

Nginx is a popular web server and reverse proxy server that is known for its high performance and scalability. It is widely used by many websites and web applications to handle a large number of concurrent connections efficiently. One of the key features of Nginx is its ability to cache dynamic content using FastCGI caching.

What is FastCGI caching?

FastCGI caching is a technique used by Nginx to cache the responses from FastCGI servers, such as PHP-FPM, to improve the performance of dynamic websites. When a request is made to a FastCGI server, Nginx can cache the response and serve it directly to subsequent requests without having to reprocess the request.

This can significantly reduce the load on the FastCGI server and improve the response time for subsequent requests. FastCGI caching is especially useful for websites that have a lot of static content or content that doesn't change frequently.

The fastcgi_cache_bypass directive

The fastcgi_cache_bypass directive is a powerful tool that allows you to control when Nginx should bypass the FastCGI cache and fetch the response directly from the FastCGI server. By default, Nginx will cache all responses from the FastCGI server, but there are situations where you may want to bypass the cache.

For example, let's say you have a website that displays personalized content based on the user's preferences. In this case, you wouldn't want to cache the responses because each user will see different content. By using the fastcgi_cache_bypass directive, you can tell Nginx to bypass the cache for requests that require personalized content.

The fastcgi_cache_bypass directive can be used in conjunction with the if directive to specify the conditions under which the cache should be bypassed. Here's an example:

location ~ .php$ {
    fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
    fastcgi_cache my_cache;
    fastcgi_cache_bypass $cookie_nocache $arg_nocache;
    fastcgi_no_cache $cookie_nocache $arg_nocache;
    ...
}

In this example, Nginx will bypass the cache if the request contains the "nocache" query parameter or if the "nocache" cookie is set. This allows you to selectively bypass the cache for specific requests.

Conclusion

The fastcgi_cache_bypass directive is a powerful tool that allows you to control when Nginx should bypass the FastCGI cache. By using this directive, you can ensure that the cache is only used for requests that can be cached, while bypassing the cache for requests that require personalized or dynamic content.

For more information about FastCGI caching and how to configure Nginx for optimal performance, please visit Server.HK.