Rails.cache & key-based expiry (Solid Cache)

fresh_when skips the render. Rails.cache skips the WORK.

Conditional GET saves you from re-sending bytes the client already has. It doesn't save you from re-computing the payload when the ETag DOESN'T match, or when the caller is another service (no browser cache, no If-None-Match) that always needs a fresh response body. For that, Rails gives you a general-purpose cache: Rails.cache.fetch(key) { expensive_work }.

fetch checks the cache for key first. A hit returns the cached value — the block never runs. A miss runs the block, stores the result under key, and returns it. One method, both branches.