[mnutt]

In varnish, if you have some requirements flexibility you can enable grace mode in order to serve stale responses but update from the origin, and avoid long requests every [5] seconds.

Not quite the same layer, but in node.js I’m a fan of the memoize(fn)->promise pattern where you wrap a promise-returning function to return the _same_ promise for any callers passing the same arguments. It’s a fairly simple caching mechanism that coalesces requests and the promise resolves/rejects for all callers at once.