Caching API responses smartly using Vary headers.

so, im trying to make some high-traffic apis better and was thinking about caching strategies. we're currently looking at using `vary` headers to let us have different cached responses based on request headers like `accept-language` or `user-agent`. has anyone really done this a lot. what were the gotchas or best practices you found for managing `vary` in a distributed caching setup, im curious about potential cache stampedes or complexities in invalidation