Content caching

In the CDN resource settings, you can enable content caching to temporarily store the file copies loaded from origins. There are two types of caching:

• On CDN servers located at the points of presence.
• In client browsers.

Caching on CDN serversCaching on CDN servers

If CDN server caching is enabled for a resource, files are copied from origins to the server cache in the following cases:

• File the user has requested from the CDN resource is not yet cached on the responding sever.
• Lifetime of the file’s copy cached on the CDN server has expired, and the file stored on the origin has changed (otherwise, the lifetime is prolonged for the same duration).
• You prefetched files from origins to the CDN server cache in the CDN resource settings.

Cache lifetimeCache lifetime

Until the cache lifetime expires, the CDN server returns a cached copy of the file to the clients without accessing origins.

You can choose one of two modes to define the cache lifetime:

Mode	Description
Same as origin	The file is cached for the period specified in the origin's response to the request. The origin must add to the response the Cache-Control HTTP header with the max-age (specifies the cache lifetime in seconds) and public (allows file caching at any level) directives. If the origin responded with the 200, 201, 204, 206, 301, 302, 303, 304, 307, or 308 HTTP status code but the response includes no header meeting the above conditions, the file is cached for the period specified in the resource settings. Files from responses with other status codes are not cached if the header is missing.
Custom	The default cache lifetime is specified in the resource settings. It applies to all the origin responses with the 200, 206, 301, and 302 HTTP status codes. For any status code (regardless of whether it's listed above or not), you can separately specify the cache lifetime that takes precedence over the default time. If a status code is not included in the list and no cache lifetime is specified for it separately, a file from the response with such a code is not cached.

Caching in browsersCaching in browsers

If caching in browsers is enabled for a resource, CDN servers will add the Cache-Control header with the max-age (indicates the cache lifetime in seconds) and public (allows file caching at any level) directives to responses with the 200, 201, 204, 206, 301, 302, 303, 304, 307, and 308 HTTP status codes. The cache lifetime is specified in the resource settings.

Files from responses with other status codes are not cached.

Cookies and query parametersCookies and query parameters

Requests to the CDN server may contain the same path in the URI but different cookies (the Cookie HTTP header) and/or different query parameters.

Query parameters that are considered during caching form part of the cache object key. Requests with different values for these parameters correspond to different cache objects. Parameters ignored during caching do not form part of the key: requests that differ in these parameters only correspond to the same object.

You can select one of the following query parameter caching modes in the resource settings:

Mode	How to treat query parameters in cache key
Do not cache	Ignore all query parameters. For requests with the same path, a single file copy is saved, regardless of the parameter values.
Cache all	Consider all query parameters. A separate file copy is saved for each unique set of parameters.
Cache all except	Ignore specified query parameters, consider the others.
Cache only	Consider only specified query parameters, ignore the others.

For example, if you select Cache only and specify the segment parameter, the same cache object will correspond to the /file.m3u8?expires=1&segment=1 and /file.m3u8?expires=2&segment=1 requests. And another object will correspond to /file.m3u8?expires=1&segment=2.

Caching of responses to requests with cookie files is configured separately using the Ignore option. If this option is off, responses to requests with the Cookie header are not cached, and the files get re-requested from the origin. If this option is on, responses get cached, and the CDN server can return files from the cache.

Cache prefetchingCache prefetching

You can forcibly (manually) fetch individual files from sources into the CDN server cache before they are requested by clients. We recommend prefetching large files of 200 MB or more.

You can only prefetch the cache for content that is not yet available on CDN servers. To update cached files, you need to purge the cache first.

There are technical limits on cache prefetching.

Purging cachePurging cache

You can delete cached file copies from CDN servers by purging the cache. This lets you quickly update in the CDN the content that has changed in the origins.

You can purge cache either fully or partially. Partial purge is recommended: if you delete copies of all files from the cache, CDN servers will significantly increase the load on the origins, having to access them at every file request.

For partial purging, you can specify paths to individual files and folders. Each path must start with /.

Examples of paths:

If the file is cached with all or some query parameters duly considered, all copies of the file get deleted by default. To delete only specific copies, explicitly state the values of query parameters included in the cache key. Here is an example: /image/foo.png?id=12345.

Use casesUse cases

• Enabling a blue-green and canary deployment of web service versions
• Publishing game updates using Yandex Cloud CDN

Useful linksUseful links

• Caching setup guide
• Cache prefetching guide
• Cache purging guide