Downstream caching refers to the caching instructions associated with objects sent with responses to clients, such as browsers, mobile devices, or client proxies.
In the Downstream cacheability section, you can decouple caching in the last mile from the browser caching settings. When doing so, you can choose whether to use the headers sent by your origin to control caching behavior or have the headers and their values controlled by edge servers.
By default, Akamai calculates the downstream caching lifetime
based on your API-level caching instructions or your origin caching headers. If your
API-level caching behavior is set to No store or Bypass cache, edge
servers attempt to prohibit downstream caching by sending so-called cache-busting
headers to clients. Cache-busting headers include
You can implement one of the following downstream caching options:
- Allow caching
- Allow downstream caching, choose the caching lifetime policy and
the headers that edge servers should send to clients. You can configure the
cache lifetime policy in relation to the settings in your origin headers or edge
servers’ time-to-live (TTL), specify a fixed maximum age value, or calculate the
lifetime based on the origin
Cache-Controlheader. For more details on these options, see Cache lifetime options. You can also apply the Mark as private directive that prevents sensitive data from being stored in shared caches.
- Allow caching, require revalidation (no-cache)
- Allow downstream caching with a mandatory origin revalidation before
a cached copy reaches the request sender. While the standard Allow
caching option only revalidates with the origin once an object’s
TTL has expired, this option forces the browser to send an
If-Modified-SinceGET request every time it requests an object. If the object has changed since the last time it was cached, the origin server sends the new version; otherwise, the origin sends an HTTP 304
Not Modifiedresponse. You can also apply the Mark as private directive that prevents sensitive data from being stored in shared caches.
- Don’t allow caching (bust)
- Send cache-busting headers downstream to prohibit downstream caching.
- Pass cacheability headers from origin
- Apply your origin’s
Expiresheader settings to downstream clients. Your origin cache headers will be passed to clients without any alteration.
- Don’t send headers, apply browser defaults
- Don't send any caching headers and let client browsers cache content according to their default settings. The default settings may vary from browser to browser.