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Cloudflare에서는 자체 NGinx 모듈로 server push를 제공하고 있는 것으로 추정됨
upstream module 에서는 HTTP/2를 지원 안 함.
But what is the point of HTTP/2 on the backend side? Because as you can see from the benchmarks, there’s not much benefit in HTTP/2 for low‑latency networks such as upstream connections.
Also, in NGINX you have the keepalive module, and you can configure a keepalive cache. The main performance benefit of HTTP/2 is to eliminate additional handshakes, but if you do that already with a keepalive cache, you don’t need HTTP/2 on the upstream side.
There is almost no sense to implement it, as the main HTTP/2 benefit is that it allows multiplexing many requests within a single connection, thus [almost] removing the limit on number of simalteneous requests - and there is no such limit when talking to your own backends. Moreover, things may even become worse when using HTTP/2 to backends, due to single TCP connection being used instead of multiple ones.