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I've always had a great a time using Fastly (varnish) for caching.

You can cache a lot more than you think if you mastermind your strategy.

A diagram of fastly/varnish state -> https://www.integralist.co.uk/images/fastly-request-flow.png

I was spec-ing out Varnish for a project recently and was really impressed with what it could do. The stale-while-revalidate approach (immediately serve data past the `ttl` for a `grace` period while asynchronously refreshing it) keeps data flowing. It can `keep` data past the `grace` period and serve that when the origin goes down or use that in conditional requests (If-Modified-Since) to the origin to prevent fetching unchanged content. Coalescing requests mitigates thundering herds that reach stale caches. VCL scripting makes the whole thing very configurable. I think Varnish needs better marketing, but I suppose Fastly does that now.

[1] https://www.varnish-software.com/developers/tutorials/http-c...

[2] https://info.varnish-software.com/blog/request-coalescing-an...

[3] https://docs.varnish-software.com/tutorials/object-lifetime/

[4] https://www.varnish-software.com/developers/tutorials/varnis...

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