Web proxy caching stores HTTP responses locally and serves them to subsequent requestors without fetching from the origin. The hit rate — the proportion of requests served from cache — determines how much bandwidth is actually saved. Understanding what drives hit rate means understanding HTTP caching semantics. Cache-Control directives that matter at the proxy layer HTTP caching is controlled by the Cache-Control response header. The directives most relevant to a forward proxy cache: Cache-Control: max-age=3600 # Cache for 3600 seconds Cache-Control: no-cache # Revalidate with origin before serving Cache-Control: no-store # Do not cache at all Cache-Control: private # Cache only in browser, not proxy Cache-Control: s-maxage=86400 # Proxy-specific max-age (overrides max-age for shared caches) Cache-Control: must-revalidate # Must revalidate on expiry, no stale serving Enter fullscreen mode Exit fullscreen mode The private directive is the most common reason proxy cache hit rates are lower than expected.…