![]() ![]() In other words, web browsers might cache the assets but they have to check on every request if the assets have changed (304 response if nothing has changed). Caches can however eliminate downloads if the resources haven't changed. ![]() If a proper ETag (validation token) is present as a result, no-cache incurs a roundtrip in an effort to validate cached responses. No-cache shows that returned responses can't be used for subsequent requests to the same URL before checking if server responses have changed. HTML pages with private user info can be cached by a user's browser but not by a CDN). On the contrary, a response marked private can be cached (by the browser) but such responses are typically intended for single users hence they aren't cacheable by intermediate caches (e.g. max-age) shows that a response is cacheable anyway. In most cases, a response marked public isn't necessary, since explicit caching information (e.g. They are as follows: public vs privateĪ response that is marked public can be cached even in cases where it is associated with an HTTP authentication or the HTTP response status code is not cacheable normally. These settings are referred to as response directives. Cache-Control: private, max-age=0, no-cache The HTTP specification enables the server to send several different Cache-Control directives which control how and for how long individual responses are cached by browsers among other intermediate caches such as a CDN. Requests that don't need server communication are considered the best requests: local copies of the responses allow the elimination of network latency as well as data charges resulting from data transfers. Cache-Control directives control who caches the response, under what conditions and for how long. Cache-ControlĮvery resource can define its own caching policy via the Cache-Control HTTP header. Let's shift our focus to the kind of headers you should be concerned about. ETag or Last-Modified header), and a lack of explicit freshness info, it will usually (but not always) be considered uncacheable. In cases where there is no validator present (e.g. A fresh representation is available instantly from a cache while a validated representation rarely sends the entire representation again if it hasn't changed. HTTP cache headers explainedĬaches work with content mainly through freshness and validation. In case you are looking for in-depth information on the role of HTTP cache headers in the modern web, here's everything you need to know. This article highlights important information on HTTP caching headers and associated CDN behavior. ![]()
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