The fastly article on the topic does a great job of explaining what surrogate keys are. I suggest familiarising yourself with it before continuing.
TLDR; the Surrogate Keys
response header is a space delimited list of "tags" for that given response.
Using surrogate keys we can more precisicely purge specific sets of reponses from the fastly cache. For exmaple we could choose to purge all CMS template, or CMS resource centre templates, or simply all CMS pages with a single column upsell element.
I've compiled a short list of keys that in combination could provide the desired level of automate cache purging granularity.
- language
- static archtype (home, visual brief, social sharing)
- cms archtype (product, promo, resource centre ...)
- cms cells/elements
Some of these are easier than others to achieve.
An example response could look like Surrogate Keys: de cms/archtype/product cms/element/faq cms/element/...