How Nginx Caches Content: Core Principles and Practical Mechanisms

Nginx caching leverages the temporal locality principle by storing copies of previously accessed content on the server, allowing subsequent requests to be served locally, which reduces network traffic, alleviates congestion, lowers latency, and improves user experience. Cached copies also keep services available when the backend server fails, enhancing robustness.

Web Cache Core Idea

The basic idea of web caching is to create local replicas of content that clients have already requested, so that repeated accesses within a short period do not need to travel to the backend server.

Nginx Cache Implementation

Proxy Store Based Cache

When Nginx receives a request for a resource that is not present locally, it generates a 404 error, captures the error, forwards the request to the backend, returns the response to the client, and stores the response on the server for future use.

Resource‑Not‑Found Driven

This method is functionally similar to the 404‑driven approach but uses an if condition inside a location block to trigger caching without producing a 404 error.

Configuration snippet:

Both mechanisms cache only responses with a 200 status and do not support dynamic query strings (e.g., getsource?id=1 and getsource?id=2 returning the same resource). Consequently, Nginx is often paired with Squid to achieve full‑featured caching.

Memcached Based Cache

Memcached allocates a memory region and builds a hash table to store cached data as key/value pairs. The server computes the hash of a key to determine its location, and the client queries the appropriate server to retrieve the data.

That concludes the overview of Nginx server caching.