> For the complete documentation index, see [llms.txt](https://docs.ionos.com/cloud/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ionos.com/cloud/~/revisions/AMiYziCllTKB2y2lmONY/network-services/cdn/overview/caching.md). # Caching Caching in CDN refers to storing copies of web content at multiple edge servers across various geographical locations. It allows users to access content from a server that is geographically closer to them, improving the speed and efficiency of content delivery. ## Features * **Static Content Caching:** Static content like HTML, CSS, JavaScript files, images, and videos are cached in the CDN edge servers. Caching is based on the request method `GET` or `HEAD` and the `HTTP` response code defined in the cache policy. There will be no differences between static content and dynamic content. Content that should not be cached must have defined cache control headers. * **Dynamic Content Caching:** With `cache-control` headers, you can customize the cache behavior to your needs and on enabling **Caching** on a CDN route, everything that matches the cache policy will be cached including the dynamic content. * **Cache Policy:** The default cache policy for IONOS CDN is as follows: * The edge servers cache all content with status code `HTTP 2xx` from the origin server for 24 hours if no cache control headers are given. Cache-control headers take precedence otherwise. * Content with `HTTP` `301`, `302`, or `404` will be cached for 10 minutes if no `cache-control` headers are set. * Stale content will be provided if the origin is unreachable and the cache still exists. * **Automatic Purging:** The CDN can automatically remove cached content based on a defined policy, ensuring that users always receive the most up-to-date version of the content when necessary. ## Cache response headers With IONOS CDN, you can set cache response headers to `X-CDN-Cache-Status` indicating whether a resource is cached or not. The supported values are as follows: * **HIT:** The resource was delivered from the CDN cache. * **MISS:** The resource was not found in the cache; it was served from the origin web server and cached. Further requests may be cached if the cache policy matches. * **STALE:** The resource was served from the cache but could have expired. Stale content will be delivered if the CDN is updating the content. A timeout or error from the origin server is provided. * **BYPASS:** All responses where the cache is disabled due to the policy or configuration. You can also ensure not to cache specific requests if the following requirements are met: * An `X-Accel-Expires` response header field was sent with a value of `0`. * An “Expires” response header was sent with a date that is already expired. * The “Cache-Control” header has values like `no-cache`, `no-store` or `private` in the response. * The response header includes the `Set-Cookie` field. * If the response header includes the `Vary` field with the special value `*`. ## Benefits * **Reduced Latency:** CDNs serve content from the nearest edge server, minimizing the distance data has to travel, reducing latency, and improving load times. * **Enhanced Availability:** Cached content can still be served to the users even if the origin server experiences downtime, improving the availability of web services. * **Content Relevance:** With well-defined caching policies, you can ensure users receive up-to-date content even while serving content from the cached server instead of the origin server. * **Scalability:** Caching allows websites to handle higher data traffic without degradation in the content served to the user requests, making it easier to scale during traffic spikes. * **Improved Security:** By reducing the number of direct content requests to the origin server, caching helps mitigate certain vulnerabilities and provides an additional security layer. --- # Agent Instructions This documentation is published with GitBook. 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