proxycaches

Proxy caches are intermediary storage layers in proxy servers that store copies of HTTP responses to serve future requests more quickly, reduce bandwidth, and improve user experience. They are used in forward proxies, which sit between clients and the wider internet, and in reverse proxies, which sit in front of origin servers or as part of content delivery networks.

Operation is straightforward: when a client requests a resource, the proxy checks its cache for a fresh copy. If a valid cached response exists, it is served directly. If not, the proxy forwards the request to the origin server, returns the response to the client, and may store a copy in its cache for later use. Cacheability relies on HTTP headers and status codes. Cache-Control, Expires, and ETag determine freshness, while Last-Modified helps validators. Shared caches use s-maxage, while private caches do not. Content validity is maintained via revalidation: a cached response can be deemed stale and revalidated with the origin via If-Modified-Since or If-None-Match. If the origin confirms no change (304 Not Modified), the cached copy is updated or extended; otherwise a new response is stored.

Management and policies include manual purge or automatic invalidation, and strategies based on TTLs and validations. Security and privacy considerations arise because caches may store sensitive data; HTTPS reduces caching opportunities unless TLS terminators are used with proper configurations. Proxy caches are a core component of many content delivery strategies and work alongside origin servers to improve performance and scalability.