HTTP caching and CDNs — designing Cache-Control
This chapter organizes the directives of Cache-Control by "who it applies to", "how long it stays fresh", and "what to do after expiry", and derives caching designs from the nature of the resource. It covers the differences between no-cache and no-store, max-age and s-maxage, where stale-while-revalidate and immutable belong, and why Vary is needed.