The proxy caching flow involves several steps, from receiving a client request to serving a response from the cache or the backend server.
1. Client request:
A client sends an HTTP request to the Nginx server.
2. Nginx Configuration:
Nginx is configured to act as a reverse proxy, and caching directives are set in the configuration file, specifying how caching should be handled.
3. Checking the cache:
Upon receiving a request, Nginx checks its cache to determine if the requested resource is already cached. The cache key is generated based on directives such as proxy_cache_key and includes components like the host, URI, and query string.
4. Cache hit:
If the requested resource is found in the cache, and the cache is considered valid based on the proxy_cache_valid directive, Nginx serves the cached content directly to the client. This results in a faster response time and reduces the load on the backend server.
5. Cache miss:
If the requested resource is not found in the cache or the cached content is considered stale (based on the proxy_cache_valid directive), Nginx forwards the request to the backend server.
6. Backend server request:
Nginx acts as a reverse proxy and forwards the client request to the backend server.
7. Backend server response:
The backend server processes the request and generates a response.
8. Storing in cache:
If caching is enabled and the response from the backend server is cacheable, Nginx stores the response in its cache for future use. The cache is updated based on the cache key and caching directives.
9. Returning response to client:
Nginx returns the response received from the backend server to the client. If the response was cached, it may include headers such as X-Proxy-Cache to indicate whether the content was served from the cache or fetched from the backend.
10. Cache control directives:
Nginx uses cache control directives like proxy_cache_valid to determine the expiration time for cached content. These directives define how long the content should be considered fresh before Nginx revalidates it with the backend server.
In summary, By following this caching flow, Nginx optimizes the delivery of content by serving cached responses when possible, reducing the load on backend servers and improving overall system performance. The effectiveness of the cache depends on the configuration, cache control directives, and the nature of the application being served.