In Nginx, the directive fastcgi_cache_use_stale controls how a server responds when it encounters certain situations while trying to use the FastCGI cache:
- FastCGI server unavailable: If the server cannot connect to the FastCGI server that processes the request, fastcgi_cache_use_stale determines if it can deliver a stale (outdated) cached version of the content instead of an error message.
- Processing errors: If there are errors during communication with the FastCGI server, fastcgi_cache_use_stale can be used to serve a stale cached response rather than failing the request entirely.
- Cache update in progress: When the cached content is being updated in the background, fastcgi_cache_use_stale allows serving the existing cached version while the update finishes.
By default, fastcgi_cache_use_stale is set to off, meaning Nginx won’t use stale content in any of these scenarios. However, enabling it with specific parameters (like error or updating) allows Nginx to deliver a potentially outdated version under particular circumstances, which can be preferable to a complete service outage for users.
Here are some resources you can refer to for more details:
Nginx documentation on fastcgi_cache_use_stale: https://nginx.org/en/docs/http/ngx_http_fastcgi_module.html
Feel free to discuss about fastcgi_cache_use_stale. We should learn to make our work not hard.