CDN-Cache-Control: Precision Control for your CDN(s)
Today we are thrilled to announce our support of a new set of HTTP response headers that provide surgical control over our CDN’s caching decisions. CDN-Cache-Control allows customers to directly control how our CDN behaves without affecting the behavior of downstream or upstream caches.
You might be thinking that this sounds a lot like the Cache-Control header we all know and love. And it’s very similar! CDN-Cache-Control has exactly the same directives as the Cache-Control header. The problem CDN-Cache-Control sets out to solve is that with Cache-Control, some directives are targeted at specific classes of caches (like s-maxage for shared caches), while other directives are not targeted at controlling any specific classes of intermediary caches (think stale-while-revalidate). As these non-specific directives are returned to downstream caches, they’re often not applied uniformly. This problem is amplified as the number of intermediary caches grows between an origin and the client.
For example, a website may deploy a caching layer on the origin server itself, there might be a cache on the origin’s network, the site might use one or more CDNs to cache content distributed throughout the Internet, and the visitor’s browser might cache content as well. As the response returns from the origin, each of these layers must interpret the set Cache-Control directives. These layers, however, are not guaranteed to interpret Cache-Control in the same way, which can cause unexpected behavior and confusion.
