alt Hacker NewsAs is traditional with most explanations of HTTP caching, it doesn't mention Vary header. Although apparently some CDNs (e.g. Cloudflare) straight up ignore it for some reason [0].
Replies
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/
Vary is Very important.
> the cache MUST NOT use that stored response without revalidation unless all the presented request header fields nominated by that Vary field value match those fields in the original request
You’ll find that some have creative readings of MUST NOT.
There was a recent discussion on X about this that had a couple of Cloudflare people chip in, including their CTO:
https://xcancel.com/simonw/status/1988984600346128664