Updated the article with some information on the `Vary` and `No-Vary-Search` headers. I’ve left out the details of how revalidation works with `Vary` since I haven’t been able to reconcile yet what the spec seems to encourage vs what the tests on cache-tests.fyi suggest is conformant behavior.
As many have pointed out here, the nature of caching has changed in the current climate of ubiquitous HTTPS, and I want to add a paragraph or two about it. Is there a good summary somewhere that I could reference? What are the the usual, most prevalent uses of HTTP intermediaries involving caches, besides CDNs and origin-controlled caches (eg Varnish)?
Good call! Honestly I just wanted to wrap it up before the holidays, but you’re right that a small section on Vary would have been useful.
Things like non-conforming caching services made me punt actual suggestions to a later article, as I wasn’t sure how my sense of the RFC interacted with the real world. HTTP Caching Tests seems like a great resource for this, but only includes Fastly out of the big providers, and it seems to be doing okay with Vary. https://cache-tests.fyi/
I’m sorry you didn’t get anything out of it. I wasn’t operating at the edge of caching knowledge, just a person refreshing and clarifying for themselves how caching works. Some things were new to me, and after spending so much time with the RFC, I just thought others may benefit or, more selfishly, would point out errors or ways to make it better.
I mean, do those <meta> tags really suggest someone who’s into SEO? Call me stale but what I really want is validation :-)